Plant your feet shoulder-width apart right before you swing at slow balls. Your feet need to be still when the racket hits the ball, not moving. This stable base is what separates clean contact from off-balance mishits.
Chapters
Tip number 2 is get a stable base on the contact. If you've got the time, there's no reason you should be off balance. So you've done the little steps and now you set, set your feet when the ball has bounced and they're in a position so that you hit. If you are not moving with the feet and then you end up leaning and rushing and you're off balance, more than likely your swing contact won't be consistent. So tip number 1 was the fast feet, tip number 2 stabilize the base nice. Doesn't have to be a really wide wide base. It can be shoulder width, but make sure the feet are planted when you hit that contact. Now, this is obviously very different if the ball comes fast, or it, it's off a tricky shot, or it comes off the fence. You want to have sharp feet and not hit a stable base too early. But here, the ball is easy to read, it's slow. Set your base just before you're going to swing and make contact.