To win a chess game one must do two things:
1)Determine what piece or pieces are most critical to your opponent's defense, and
2)Destroy it (sometimes forcing the piece or pieces to move is as or even more effective than capturing the piece).
This is the heart of the game. In order to do this it is necessary to have an acute sense of what is happening on the board, and what functions the different pieces deployed by the opposing player have in the peculiar game you are playing. If you do not understand why your opponent has made the moves he or she has made, you will not be able to understand their plan, and if you do not understand their plan, you will not be able to resist them when they strike.
There are four questions you must ask yourself before making a move:
1)Why did my opponent make the last move?
2)What is the weak point in my opponent's defense and how can I destroy it?
3)What is the weak point in my defense and how can I protect it?
4)What is my opponent planning to do on the next move, and how can I ruin his or her plan?
Tempo is also key. Most games are won or lost based on tempo, which means achieving the maximum strategic development of your pieces in the smallest number of moves. If you have a significant tempo advantage over your opponent, you will probably win the game. Tempo is probably the most important strategic concept in chess.
If you ask and can answer these four questions, chances are you will be successful at chess more often then not. These are not easy questions to answer, but answering them is key to good chess play.