Which book should I read first?

My suggestion would be that you look at available samples and pick the one that most interests you. Silman says that his book is for those from 1000 to 1600.
https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf
https://www.silmanjamespress.com/shop/chess/amateurs-mind-the-2nd-edition/
"... [Simple Chess by Stean] is very good, and will definitely help players in the general rating range of 1300-2000 with their positional play and strategic thinking. …"
https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf

IMO - read Stean's "Simple Chess" prior to Silman's "The Amateurs Mind". (Sorry Danny, although I can understand where you are coming from. The choice of which to read first is certainly subjective).
While the reading order can legitimately be viewed as a matter of personal preference, I recommend to follow the reading order outlined in the following article. I have endeavored, after a lot of thought, to present the reading sequence such that the more basic books, which introduce elemental positional concepts are to be read first. That is, the treatment in the books tend to build in sophistication and complexity as you progress in the sequence presented. Nevertheless reading Silman before Stean may work better for some than others. In fact, one may choose to read selected portions of both books at the same time, as the interest strikes you. Finally (and for what it's worth) the text of "The Amateur's Mind" ends at p.443, - there is no index. The text of "Simple Chess" ends at p.160 - also no index.
Good Positional Chess, Planning & Strategy Books for Beginners and Beyond...
https://www.chess.com/blog/RussBell/introduction-to-positional-chess-planning-strategy

My suggestion would be that you look at available samples and pick the one that most interests you. Silman says that his book is for those from 1000 to 1600.
https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf
https://www.silmanjamespress.com/shop/chess/amateurs-mind-the-2nd-edition/
"... [Simple Chess by Stean] is very good, and will definitely help players in the general rating range of 1300-2000 with their positional play and strategic thinking. …"
https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf
I generally agree with the idea of perusing samples of the books in question and then making up one's mind about which to read first....that is, of course, if samples are available. Of the two books, Amazon on its product web page has a "Look Inside" feature which allows viewing of portions of Stean's "Simple Chess". An ebook of the book is also available for reading here...
https://archive.org/details/Simple_Chess_New_Algebraic_Edition
Amazon does not have the "Look Inside" feature for "The Amateur's Mind".
However one can read and/or download copies of both books on Scribd.com if one has a subscription to the site (or takes advantage of their free trial offer).
https://www.scribd.com/book/271528655/Simple-Chess-New-Algebraic-Edition
https://www.scribd.com/search?content_type=tops&page=1&query=the%20amateur%27s%20mind%20jeremy%20silman&language=1
https://www.chess.com/blog/RussBell/scribd-com-for-online-chess-book-reading
I also agree that "Simple Chess" is accessible for those rated above about 1300.
However, I don't agree that "The Amateurs Mind" is appropriate for anyone below that same rating level, in spite of the fact that in the book Silman does analyze games with players rated as low as 1000. I own the book, and in my opinion "The Amateurs Mind" is generally too difficult for players rated below about 1300-1400. This because the book assumes a level of understanding and skill with positional concepts and techniques that those rated below 1300 are unlikely to have acquired.
Bottom Line - IMO, the Silman and Stean books are appropriate for players rated above 1300, minimum. And I recommend that Stean's "Simple Chess" be read prior to Silman's "The Amateur's Mind", for the reasons given in my earlier post.
… Amazon on its product web page has a "Look Inside" feature which allows viewing of portions of Stean's "Simple Chess". ...
One can also go to the google preview at the dover publication site in order to see a substantial portion of the book:
https://store.doverpublications.com/0486424200.html
A fair amount of book-quoting can be seen in the review at:
https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf
… Amazon does not have the "Look Inside" feature for "The Amateur's Mind". ...
A substantial sample can be viewed at:
https://www.silmanjamespress.com/shop/chess/amateurs-mind-the-2nd-edition/
Again, there is a review with book-quoting included:
https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf

IMO - read Stean's "Simple Chess" prior to Silman's "The Amateurs Mind". (Sorry Danny, although I can understand where you are coming from. The choice of which to read first is certainly subjective).
While the reading order can legitimately be viewed as a matter of personal preference, I recommend to follow the reading order outlined in the following article. I have endeavored, after a lot of thought, to present the reading sequence such that the more basic books, which introduce elemental positional concepts are to be read first. That is, the treatment in the books tend to build in sophistication and complexity as you progress in the sequence presented. Nevertheless reading Silman before Stean may work better for some than others. In fact, one may choose to read selected portions of both books at the same time, as the interest strikes you. Finally (and for what it's worth) the text of "The Amateur's Mind" ends at p.443, - there is no index. The text of "Simple Chess" ends at p.160 - also no index.
Good Positional Chess, Planning & Strategy Books for Beginners and Beyond...
https://www.chess.com/blog/RussBell/introduction-to-positional-chess-planning-strategy
No worries, Russ, it is subjective. The reason I think The Amateur's Mind may be better to read first is because Silman gives a lot of bulletpoints for the amateur, and goes into amateur-style thought processes, whereas Stean is more generally an instructional book of strategic themes based on high-level games with lots of moves given without explanation, though when he does explain, it is very good. Probably the order doesn't matter too much, but I can relate to that level of reading granularity in my own life where time is of the essence and you don't want to spend months reading one book realizing that you should have read or done something else first. In this case, it probably doesn't matter in the grand scheme of things.

take a look at aron nimzowitsch's "my system" it's a classic in positional chess, and it was studied by the young tigran petrosian every night before he went to bed

IMO - read Stean's "Simple Chess" prior to Silman's "The Amateurs Mind". (Sorry Danny, although I can understand where you are coming from. The choice of which to read first is certainly subjective).
While the reading order can legitimately be viewed as a matter of personal preference, I recommend to follow the reading order outlined in the following article. I have endeavored, after a lot of thought, to present the reading sequence such that the more basic books, which introduce elemental positional concepts are to be read first. That is, the treatment in the books tend to build in sophistication and complexity as you progress in the sequence presented. Nevertheless reading Silman before Stean may work better for some than others. In fact, one may choose to read selected portions of both books at the same time, as the interest strikes you. Finally (and for what it's worth) the text of "The Amateur's Mind" ends at p.443, - there is no index. The text of "Simple Chess" ends at p.160 - also no index.
Good Positional Chess, Planning & Strategy Books for Beginners and Beyond...
https://www.chess.com/blog/RussBell/introduction-to-positional-chess-planning-strategy
No worries, Russ, it is subjective. The reason I think The Amateur's Mind may be better to read first is because Silman gives a lot of bulletpoints for the amateur, and goes into amateur-style thought processes, whereas Stean is more generally an instructional book of strategic themes based on high-level games with lots of moves given without explanation, though when he does explain, it is very good. Probably the order doesn't matter too much, but I can relate to that level of reading granularity in my own life where time is of the essence and you don't want to spend months reading one book realizing that you should have read or done something else first. In this case, it probably doesn't matter in the grand scheme of things.
Danny - I have no issues with anything you said here. Bottom line - one can read either book first (Amateur's Mind or Simple Chess), as preferred, but I think we both agree that both books are recommended.

take a look at aron nimzowitsch's "my system" it's a classic in positional chess, and it was studied by the young tigran petrosian every night before he went to bed
My System is certainly worth taking a look at. It was THE book on positional chess concepts when Tigran Petrosian was young (born 1929)! And still instructive today....in spite of some controversy....
Perspective on Aron Nimzowitsch's "My System"...
https://www.chess.com/blog/RussBell/perspective-on-my-system-by-aron-nimzowitsch
One can get some idea of the lasting scope of the respect for My System by looking at:
https://www.chess.com/article/view/the-best-chess-books-ever
Still, it might be noted that My System apparently did not occur to GM Yasser Seirawan as something to include in his list of personal favorites, and Aaron Nimzowitsch was not identified by the GM as a very worthy author.
https://www.chess.com/blog/RoaringPawn/an-open-letter-to-the-four-time-us-chess-champion-gm-yasser-seirawan
https://www.chess.com/blog/GMYAZ/open-letter-response-user-radovics-letter-to-me
My System has accumulated some direct negative commentary over the years.
"... I found [the books of Aaron Nimzowitsch to be] very difficult to read or understand. ... [Nimzowitsch: A Reappraisal by Raymond Keene explains his] thinking and influence on the modern game in a far more lucid and accessible way. ... The books that are most highly thought of are not necessarily the most useful. Go with those that you find to be readable; ..." - GM Nigel Davies (2010)
In 2016, IM pfren wrote:
"My System is an iconoclastic book. A lot of things in there is sheer provocation, and it does need an expereienced player to know what exactly must be taken at its face value.
I love 'My System', and I have read it cover to cover one dozen times, but suggesting it to a class player is an entirely different matter."
Also: "[Some things] ARE wrong, and it's not easy for a non-advanced player to discover those wrong claims.
Nigel Short has claimed that 'My System' should be banned. Stratos Grivas says that the book is very bad. I don't share their opinion, but I am pretty sure that there are more useful reads for class players out there."
Although he is a fan of My System, IM John Watson similarly acknowledged (2013) that:
"... Not everything in it has stood the test of time, ..."
http://theweekinchess.com/john-watson-reviews/john-watson-book-review-108-of-eplus-books-part-2-nimzowitsch-classics
One last point to keep in mind is that, even if My System would eventually help a player, it might not necessarily be helpful to a player now.
"... Just because a book contains lots of information that you don’t know, it doesn’t necessarily mean that it will be extremely helpful in making you better at this point in your chess development. ..." - Dan Heisman (2001)
https://web.archive.org/web/20140626180930/http://www.chesscafe.com/text/heisman06.pdf
A My System sample can be seen at:
https://www.qualitychess.co.uk/ebooks/MySystem-excerpt.pdf
A Chess Praxis sample can be seen at:
https://www.qualitychess.co.uk/ebooks/ChessPraxis-excerpt.pdf
Various samples:
https://www.newinchess.com/media/wysiwyg/product_pdf/9027.pdf
"My System is of course one of the great masterpieces of chess literature, compulsory reading for generations of players...I recommend My System[...]as strongly as I do any other chess book. These days most classic works are no longer essential to a chess education, especially since the Internet; but if there's an exception, Nimzowitch's work is it." - from IM John Watson's book review here...
https://theweekinchess.com/john-watson-reviews/john-watson-book-review-108-of-eplus-books-part-2-nimzowitsch-classics
Perspective on Aron Nimzowitsch's "My System"...
https://www.chess.com/blog/RussBell/perspective-on-my-system-by-aron-nimzowitsch

As I mention in my blog article, I prefer the english translation of the Lou Hays' 21st Century edition of "My System", where the stilted, pedantic writing style of Nimzowitsch's original german has been purposefully avoided, making it an easily readable english language edition...
https://www.amazon.com/My-System-Century-Aron-Nimzowitsch/dp/1880673851/ref=sr_1_3?crid=2MEJJIDVVEN8V&keywords=my+system+aron+nimzowitsch&qid=1569908159&s=books&sprefix=my+system%2Caps%2C199&sr=1-3

The following is Yasser Seirawan's Introduction to the Lou Hays 21st Century Edition of Aron Nimzowitsch's "My System", published November 1991. In this introduction he describes his earlier misgivings regarding the book, then continues by praising not only the Lou Hays edition of the book, but "My System" in general....(note particularly his comments in the third from the last paragraph which begins "This then is the strength of My System......"
The following is a scathing criticism of Nimzowitsch's "My System" by Yasser Seirawan (penned in 2018, in response to an open criticism of his apparently prior vocal criticisms of Nimzowitsch, and his book)...
https://www.chess.com/blog/GMYAZ/open-letter-response-user-radovics-letter-to-me
So what are we to make of it - on the one hand Seirawan praises Nimzowitsch and his book, then later excoriates them both....
You be the judge...
… Until you can learn to eliminate major tactical mistakes from your game, positional play isn't going to mean anything.
If one makes major tactical mistakes in some games, does that mean that positional play can't help in some of the others? Can it be easier to avoid major tactical mistakes if one improves one's ability to avoid difficult positions?
… Until you can learn to eliminate major tactical mistakes from your game, positional play isn't going to mean anything.
If one makes major tactical mistakes in some games, does that mean that positional play can't help in some of the others? Can it be easier to avoid major tactical mistakes if one improves one's ability to avoid difficult positions?
There is no positional advantage worth anywhere close to dropping a queen or even a pawn for that matter. Show me any game where one side dropped material without compensation and came back to win without a mistake by the opponent. ...
Let me know if you decide that you want to answer these questions:
If one makes major tactical mistakes in some games, does that mean that positional play can't help in some of the others? Can it be easier to avoid major tactical mistakes if one improves one's ability to avoid difficult positions?