1. Material - Take good care of all your material (pieces and pawns). Before you touch anything, make sure that your next move is safe. And before capturing the enemy pieces or pawns, be careful if they are having support. And remember the values of the pieces (Q=9, R=5, B=3.5, N=3, P=1).
2. Visualize - Before actually playing any move, make it first in your mind and try to see the position. How can the opponent play then? What would be a good move for you to respond with? This is very important and MUST be done before each and every move you play.
3. Mobility - Try to keep ALL your pieces active. Most of the quick losses in the opening phase are due to bad development of pieces. So, try to develop all your pieces effectively. If you are finding it difficult to think of a good move, try to improve the position of your piece which is not doing anything useful.
4. Check and Capture - the two most powerful moves in chess! Before every move, take special care to think of all the Checks and Captures that are possible in the position. And think how to counter them.
5. Opening phase
Some of the important points to remember are:
a) Development is like a race! Try to bring out all your pieces quickly to control the Center.
b) Occupy the center with pawns. Then develop your Knights, then Bishops, do Castling and finally connect the Rooks.
c) Complete your development before attacking. Do not be in a hurry!
d) Do not waste time moving the same piece again and again. Also, do not exchange pieces unnecessarily.
e) Be careful in moving pawns. Moving too many pawns weakens the position.
6. Time - Most of the games are played with a chess clock. Balance your time properly and do not spend too much time on a single move, even if it is a difficult position. Do not play too fast either, take your time for every move. In case of time pressure, concentrate on the position and keep an eye on the clock.
7. Think - If you cannot find a satisfactory move in a position, then think more! Many games are lost due to hasty decisions. After you make up your mind on the move you want to play, spend a few more minutes to double-check if everything is ok for this move. Take your opponents moves seriously and try to think what is the idea he may have in his mind. And how can you spoil his plan?
8. Calculate - Chess is 99% tactics. Try to calculate the moves ahead in your mind before making a move. Do it slowly and try to see the position clearly in your mind. Try to recognize patterns and remember the winning techniques in each pattern.
9. Mindset - Try to be balanced and calm in your mind, irrespective of whom you are playing. If you are playing a stronger player, do not start the game thinking how you are going to face him. And if you are playing a weaker player, do not be over-confident. Try to be confident and calm irrespective of the opponent.
10. Endgame - Use the King well. Do not resign even if you are down in material. Learn your Endgame technique well and practice it often. Remember that a Draw is better than a Loss!