It's wise to approach a match with the idea of using your strengths, but don't forget to test your opponent as well. You don't want to lose a match because you didn't know about a glaring weakness in his game! This is why it's often good to scout out an opponent in advance, or ask other players about him, so you can go in knowing what his weaknesses might be. Ideally, this allows you to play your strengths against their weaknesses. But while it's difficult to win without using your main strengths, you can often win by matching your average shots against his weakness, or even your weakness against his even bigger weaknesses. (I remember once watching two players with big forehands go at it an entire match, backhand to backhand, with each player keeping the ball very wide to the others backhand so the opponent couldn't use his big forehand. So it became a battle of their weaknesses.) So test your opponents - serve long & short with different speeds and spins; test their forehand, backhand, and middle; attack at different speeds; try various types of pushes, and so on. Don't risk not knowing your opponent's weaknesses!