Originally Posted by GoudX
Against one player I attempt to keep the ball lower than 3ft above the net (or about 7ft with lots of spin to his backhand), as he can crush high forehands all day long!
Forcing your opponent to hit out of their favorite strike zone is always rewarding, unless it requires you to modify too much your own habits. Some like it high and loopy; some like it lower and fast; some like it when they don't have to move too much forward or backward; etc. Find what that is and make sure he sees as few of them as possible.
Personally, as I can generate tons of spin off both wings and use a more extreme grip on both my backhand and forehand (semi-western backhand and forehand), I thrive on high balls. Hit lower and my game is not as big as it can be -- it negates some of the effect my spin can cause. I do have answers to adapt (as I was forced to do so often), but forcing me to do so already sets you up for better situations.
If someone starts doing that to you (and you happen to enjoy higher balls), mix-in with slightly short slices. The usual flat hitter doesn't manage to hit well consistently against that and he'll sooner or later pop a sitter you can use to get the ball up in the air... actually, the power of a good slice is often underestimated with amateurs: it can draw an easy sitter from most opponents, most of the time, unless you abuse of it.