make your opponent lose
Whats the best strategy in chess?
Unless there is a tactical issue, make a move that increases the total number of legal moves you have available, and impedes your opponent's total. If you are significantly ahead, attack. If you are significantly behind, defend by moving your pieces near your king.
Develop pieces as quickly as possible. Do it faster than your opponents then most of the time you can attack first. It is simple and safe.
Always move a pawn on an odd numbered move, and a piece on an even numbered move. Oh, and only give checkmate if the move number is divisible by the number of pieces left on the board (including kings).
I've wondered about this in my about my game. I have no strategy. All I do is look for tactics (pins, skewers, etc.) and follow basic principles - control center, develop, etc.
In chess videos you hear about "King/Queen side attacks" and other real strategies. All I ever do is look for good/logical moves. Perhaps that's why I'll never be a GM. Well that, and my lack of true talent.

thanks