#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.
#2 try to hit the ball a little bit in front of you. This will also help with #1
#3 footwork - keep your feet moving. Nadal is a good example of this. Get to where you need to be to hit the ball as early as you can but dont just set your feet once there. Keep them moving so you can adjust for a funny bounce etc.
Get some lessons, I think a mix of private and group lessons is beneficial.
Try to play at least twice a week, more if you have the time.
Völkl PB10 Mid / Pro's Pro Vendetta 1.20mm @ 50lbs