Originally Posted by gmatheis
#1 - Keep your eyes on the ball - I know that sounds simple but they first key to hitting well is making good contact, and if you take your eyes off the ball before you hit it, even if it's just an instant before, you will mishit more often. So don't worry about where your ball is going, keep your focus on the hit.
Most important part of this is to keep your head still. Even if you close your eyes just before impact you can still hit the ball cleanly (at least on a hard court without any wind). If you jerk your head up, you mess up your entire body position.