How to improve my game?

What is the best way to improve my game? I am learning some openings and I review games afterward and analyze my mistakes. Other than that I just play. What should I do to get better faster?

Read Shereshevsky's Endgame Strategy.  Do a serious study of the material, repeating parts you need extra work on if necessary. 

Any other suggestions? Is that the best book to read if I only read one chess book? My standard rating is around 1450 if that makes any difference.

What kind of mistakes happen repeateadly in your games : this is probably what you have to improve first to get better ?

You may also want to have a look at this list and try and assess where you stand :

http://www.chess.com/blog/hicetnunc/chess-maturity

Work on eliminating your weaknesses. The more you do that, the more you learn about yourself. At the class level, technique carries more weight than just trying to memorize (and them mix up the move order of) opening theory.

Study tactics - it will give you ideas on how the pieces work in concert and also act as a defensive mechanism for spotting an attack against you early enough to do something about it before it's too late.

Other than that, there is no such thing as a "get rich quick" formula. What ever effort you put in will be the results you get back.

I disagree with OogieBoogie' suggestion. GM Nigel Davies told me he read that book just before he became an IM !

If you're U1800 OTB, it's doubtful this book is of any value for you, and there are probably much more important things to do first.

You should do more of the Tactics Trainer. It actually helps a lot.

I find often that I am good at getting control of the middle of the board, but as pressure builds in the middle of the game I sometimes flounder the at what seems like the "breaking point" of the position. How can I specifically address this?

When the center is a no man's land (as it usually is) then work on the flanks.  Always calculate to see if you could break the central tension (I'm assuming you mean knights on c3/c6 or f3/f6 and with Tarrasch pawn structures, or King's Indian structures with a pawn at c5 or e5 and you have e4,d4, and c4 pawns), and if you feel you'd have the better chances giving the opponent an isolated d-pawn or his trumps outweigh yours (such as it being unrealistic for you to stop a d5 advance from white, though such situations are rare)

Edit: Read it as "middle of the board" instead of game.  Sorry. 

You can improve your game by playing Russian rullete with your gun. You make a bad move, you pull the triger with 1 out of 6 bullet, next time 2 out of 6,.... So you will have 2 options left, either you start playing strong chess or you die.