As far as positioning yourself, get ready for the shot first. Its a process of
A. Striking a pose. Meaning bringing your racket back and getting ready
B. Getting to the spot. Once you have your arm up, you can gauge how much distance there should between you and the ball. and remember to position yourself behind the
C. Making your stroke.
You also want to keep your eye on the ball instead of guessing. If you can't see it, you typically can't hit it.
Hopefully this helps you!