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Try the advice in this two-part article from chess cafe. It's not sexy, but it will improve your game tremendously. Even if you think it won't.
http://www.chesscafe.com/text/skittles148.pdf
http://www.chesscafe.com/text/skittles150.pdf
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I skimmed both of these, and it is good advice.
But you also have to
play. Perhaps the author just assumes the reader will be a club player and plays rated games regularly. But if you are not, this part is important too. It's best to join a club with rated tournaments or play a lot of weekend events. It's important that the games be rated, and have a fairly slow time control, one where you record all the moves. Once the game is over you can analyze your play at home, maybe with the help of a computer program, or better yet, with your opponent just after the game. Sometimes stronger players will get involved in the post game analysis too - listen to them. This is better than the computer analysis because a computer can't really tell you
why it chooses certain moves or what it's plan is, other than in a rudimentary way.