In order to be a strong tournament player, it is crucial to improve your tactical ability and have strong endgame technique.
Jeno Ban's _Tactics of Endgames_ will help you accomplish both.
Just a few of the things you will get out of it:
1) A strong desire to improve your endgame technique. The positions in the book look simple, but once you see the subtle (and beautiful) solutions, you can't help but see the complexity in the game of chess. This will force you to look more carefully when you start to play. You will even enjoy studying the endgame, which is usually thought of as tedious and dull.
2) Improved ability to spot tactics. Because the positions are relatively simple, basic maneuvers like forks, skewers, pins, etc. will stick out in your mind. Your standard of play will improve, and you will make fewer blunders, and will be able to calculate farther ahead.
I noticed studying a few chapters improved my game very rapidly.
3) Improved defensive skills--you will begin to learn how even the most hopeless position can contain elements of poison for the superior side. Good defensive skill will make you extremely tough to beat.
Tactics of Endgames is a steal. Get the book and enjoy trouncing your opponents in the opening, middle, or endgame.