Fred Reinfeld once said, "The 3 strongest moves in chess are checks, capture and pawn promotion." I could not agree more. If your opponent can make one of these 3 moves, there's a pretty good chance they will be included in his plan. They are strong in that if you answer them insufficiently, you lose material. It is therefore important to always run through their possibilities. Is there a check? Can he capture one of your pieces? Can he create a dangerous passed pawn? Any of these 3 can show up while you're in the middle of the game so don't forget to check for them first.