(This assumes you have a functioning chess engine, but want to optimize it.)
(also if you don't know how to create a base chess engine, look up the "minimax algorithm")

-Alpha beta pruning (SUPER IMPORTANT)
-NegaScout (or principal variation)
-Iterative Deepening
-Killer Moves
-History Heuristic
-Quiescent Search
-Pawn Position Evaluation

I reccomend looking at the corresponding wiki articles for information on how 
to program these.