Anytime you work on your footwork, make sure you can feel your feet underneath you. That means getting into a position where you can easily push off and go.
You want to be up on your toes. If you’re standing on your heels, you have no stability. You shouldn’t be all the way up on your tippy toes either. Focus on getting into a wide stance over your toebox.
Footwork is the secret to great tennis.