Advice for improving my middle game

I started playing chess about a year ago, and initially my efforts were paying off.  I became more conscious of undefended pieces, learned the basics of some openings, figured out how to develop pieces / castle, etc.  John Bartholomew's videos helped a lot.

My rating went from about 800 to about 1250, and that's where I've been stuck for about 6 months.  When I'm up against people in the 1300-1400 range, they usually outmaneuver me and gain better positions.  I analyze the games later, and the engine shows that higher rated players gain a positional advantage soon after the opening and maintain it throughout the middlegame.  I think it's really cool and intriguing, and this kind of higher level strategy is one of my favorite parts of chess.

I know I still have room to improve at the basics, but I don't think that will be enough.  There's a deeper level that I'm just not grasping yet.  Anyone else been in a similar situation and have any advice?

Understanding Chess Middlegames by John Nunn will teach you the basic principles of middle games. You will discover many misconception. It's 200+ pages only.

Looks like it's geared towards 1600+, but I'll check it out.

http://www.gambitbooks.com/pdfs/Understanding_Chess_Middlegames.pdf

"... For players rates from 1700 to 2400, this book will provide ample study material to help make you a better and more knowledgeable player with sharper skills in all aspects of the game. ..." - FM Carsten Hansen (2012)

https://web.archive.org/web/20140627012322/http://www.chesscafe.com/text/hansen154.pdf

I am really just guessing, but perhaps it would make sense to consider some of these books:

The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)
https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/

Seirawan stuff:

http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner

http://www.nystar.com/tamarkin/review1.htm

50 Essential Chess Lessons by Steve Giddins
https://web.archive.org/web/20140708100833/http://www.chesscafe.com/text/review534.pdf

http://www.gambitbooks.com/pdfs/50_Essential_Chess_Lessons.pdf
Simple Chess by Michael Stean
https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf

http://store.doverpublications.com/0486424200.html
Amateur's Mind by Jeremy Silman
https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf

https://www.silmanjamespress.com/shop/chess/amateurs-mind-the-2nd-edition/

One thing you might try is to always be making a developing move, which includes:

 - moving a new piece out,

 - castling,

 - one pawn move to let out each bishop and

 - one more pawn move to help control the center.

This may seem obvious, but it's really surprising how easy it is to forget. This works wonders with piece positioning.

Basically, just refuse to do anything else if you can do something in the list.

Wow, this got way more responses than I was expecting.  Thanks for the resources and recommendations everyone.

Simple Chess, recommended by kindaspongey, sounded interesting: "this book illustrates an increasingly prevalent and successful style of play — a method that begins by slowly accumulating small but permanent advantages, saving the outright attack for later in the game."

That's a lot to think about.  Excuse me, I've got some personal work to do...