
Make sure you choose openings that fit your style. If you are a tactical player, do not choose the English opening with white, and the French Defense with black, for instance.
When you select an opening, make sure you have the time necessary to master it. Some openings, like the Sicilian Defense, are incredibly vast and complex and require countless hours to learn and understand. If you do not have the time, pick openings that are more "compact."
Do not succumb to the temptation of going after your opponent right away. Remember, the opening is the phase of the game where you are trying to deploy your forces. Whenever you are getting ready to make a move in the opening, ask yourself if it fulfills the goal of development.
Do not give up the center! Always remember the importance of the center of the chess board. Make sure your pieces are developed in such a way that they can contribute to the fight for the center which is almost sure to occur later on.
Gambits are quite common in the opening phase of the game. When you are tempted to take the pawn you are being offered, always make sure that you know what your opponent's ulterior motive is!
Your goals during the middle game are very different from those in the opening. When the time comes, make sure you take a moment to acknowledge the end of the opening phase, and set your strategy for the next phase.
Remember, the game of chess involves two players, not just you. No matter how enamored you are with your own plans, make sure you always ask yourself about your opponent's intentions.
You are not a computer. You can not calculate countless moves ahead on every single move. Develop a sense as to when you should spend a lot of thinking time calculating, and when you can get away with using your intuition.
If you are in the middle of calculating a combination, make sure you don't stop too early. Analyze in your head the final position and assure yourself that you have gone deep enough.
As obvious as this sounds, the fact is that players often forget to look at the big picture and make sure the moves they are making are part of a bigger plan. Do not make this mistake!
Remember that in the endgame the king is not a liability anymore. Instead of having to protect him, you can actually use him as a very dangerous weapon!
Now that so many pieces are off the board, you can take the time to calculate more often and deeper than before. Do not let your opponent surprise you with a move you haven't thought of!
There are many endgames that you can just not win during the game if you don't already know how. So dedicate some of your preparation to the endgame, and focus on those you are most likely to encounter.
Tournament chess revolves around time controls, and the last thing you want is to lose a game because of time. Pace yourself to make sure you will have enough time left when nearing the time control.
No matter what the result of the game was, make sure you take the time to carefully go over it. Nothing helps you learn better than your own mistakes!