Step 1: follow opening principles.
Step 2: Ask yourself questions. When an opponent plays ask: what did that piece leave behind? (Do the same thing with your own pieces BEFORE you move)
Step 3: Tactics: what piece can be pinned and how can i attack/take advantage of it? Can i deflect a piece guarding a key square? Positional play: How can i improve my pieces relative value? Can i get a passed pawn? Can i get a knight on an outpost? Can i get a bishop pair?
The list goes on and on, but start with that. Oh and the most important: If you aren't calculating your opponents next move, your going to lose.
What's your thought process when choosing a move? How do you decide which piece to move or which square to move to? How do you decide on which threat is more important and imminent? I'm sorely in need of a more systematic way of deciding moves.