skip instead of stompping. i find that the side step/skip type movement allows me to cover most the baseline without having to sprint. i can also move in diagonally quite a bit using the same footwork. Federer has very light movement, Andy Roddick is a stomper. Check out a video of Federer and just focus on his legs for a few minutes. You will see that he is very bouncy and does a lot of skipping around the court rather than just sprinting.
also, doing a small split step as your opponent hits the ball* makes it easier for you to change directions and move your body without having to be explosive or to stomp. try to move smoothly as opposed to quickly and you will find out that you have a lot of time; the tennis court is small unless you are playing someone at a very high level. Also, make sure you have proper sized tennis shoes and that they fit properly.
maybe take some ballet or dancing lessons.
* this is to be done on every shot.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM