1. e4 d5


Opening Principles:
- Control the center squares – d4-e4-d5-e5
- Develop your minor pieces toward the center – piece activity is the key
- Castle
- Connect your rooks
Tactics...tactics...tactics...
The objective of development is about improving the value of your pieces by increasing the importance of their roles. Well-developed pieces have more fire-power than undeveloped pieces and they do more in helping you gain control.
Now we will look at 5 practical things you can do to help you achieve your development objective.
They are:
- Give priority to your least active pieces.
- Which piece needs to be developed (which piece is the least active)
- Where should it go (where can its role be maximized)
- Exchange your least active pieces for your opponent’s active pieces.
- Restrict the development of your opponent’s pieces.
- Neutralize your opponent’s best piece.
- Secure strong squares for your pieces.
Don’t help your opponent develop.
There are 2 common mistakes whereby you will simply be helping your opponent to develop:
- Making a weak threat that can easily be blocked
- Making an exchange that helps your opponent to develop a piece
Pre Move Checklist:
- Make sure all your pieces are safe.
- Look for forcing moves: Checks, captures, threats. You want to look at ALL forcing moves (even the bad ones) as this will force you look at, and see the entire board.
- If there are no forcing moves, you then want to remove any of your opponent’s pieces from your side of the board.
- If your opponent doesn’t have any of his pieces on your side of the board, then you want to improve the position of your least active piece.
- After each move by your opponent, ask yourself: "What is my opponent trying to do?"
2 exd5 is the usual reaction to 1 e4 d5.


1...d5 is not the Ruy Lopez. It's the Scandinavian. If you research for the right opening, you'd probably find the right response on numerous Websites. The Ruy Lopez is 1.e4 e5 2.Nf3 Nc6 3.Bb5, in which Black is not forced to play those 2 moves. 1...d5 is one of many alternatives he has.

Is it fair to say that if either side plans to play a specific opening, they need to have a decent repertoire of various openings, because the ability to play each of them depends on the first moves of the other side?

Is it fair to say that if either side plans to play a specific opening, they need to have a decent repertoire of various openings, because the ability to play each of them depends on the first moves of the other side?
Your study time would be better spent working on tactics, opening principles, and blunder checking your moves. Openings at our level do not decide games.

It is mutually exclusive - if you don't understand an opening, memorising moves will be counterproductive. You can't understand an opening without understanding the opening principles in full, which IMBacon posted in #2.
"... the further advanced the queen becomes, the more prone it is to attack from enemy pieces, and this is particularly the case in the opening when there have been no piece trades and the board is cluttered. If you're not careful with your queen handling in the opening then you could easily lose time as it gets pushed from pillar to post. And losing time is not a good idea because you are likely to fall behind in development. ..." - GM John Emms (2006)
This is why White might prefer the result of 1 e4 d5 2 exd5 Qxd5.
Not impossible, but it is unlikely. If a game started with 1 e4 Nc6, it would be possible for a game to continue 2 Nf3 e5 3 Bb5 and end up being considered to be a Ruy Lopez (although some might add, "by transposition").
I think that you have the idea. One can get an idea of what a repertoire is like by looking at the example described in the introduction to Opening Repertoire 1 e4.
https://www.newinchess.com/media/wysiwyg/product_pdf/7819.pdf
... Your study time would be better spent ...
Alternative view available at:
https://www.chess.com/article/view/how-to-start-out-in-chess
... Openings at our level do not decide games.
So you don't want to deny that they can influence games? Are you one who obtained Chess Openings Theory and Practice as your first chess book?
It is mutually exclusive - if you don't understand an opening, memorising moves will be counterproductive. ...
In this discussion, did anyone advocate memorising without understanding?
... You can't understand an opening without understanding the opening principles in full, which IMBacon posted in #2.
For many people, is "understanding" a matter of a gradually improving process, accompanied by the examination of examples?
"... I made these for my students. When we can sit one on one, where questions can be asked, and examples givens. ..." - IMBacon (February 16, 2018)
Is it fair to say that if either side plans to play a specific opening, they need to have a decent repertoire of various openings, because the ability to play each of them depends on the first moves of the other side?
Your study time would be better spent working on tactics, opening principles, and blunder checking your moves. Openings at our level do not decide games.
"... Some here have asked for specifics, and I have tried to explain as well as I can. ..." - IMBacon (February 16, 2018)
Trying very hard to explain at the moment?

Is it fair to say that if either side plans to play a specific opening, they need to have a decent repertoire of various openings, because the ability to play each of them depends on the first moves of the other side?
The opening is determined by both players. There is no way to force any opening. 1.e4, 2.Nf3, and 3.Bb5 is not the Ruy Lopez. The Ruy Lopez is specifically 1.e4 e5 2.Nf3 Nc6 3.Bb5.
For example, 1.e4 c5 2.Nf3 Nc6 3.Bb5 is the Rossolimo Sicilian, not the Ruy Lopez.
Against various openings, 2.Nf3 and 3.Bb5 are just stupid. 1.e4 e6 2.Nf3?! d5 3.Bb5? Is just stupid. White should play 2.d4 when given the opportunity and in the French, that Bishop is your Trump card because Black has a bad Bishop. Why let Black trade it off with 3...Bd7?