I think the key to
improving your serve is really going to be your toss. Getting your toss
to be consistent is a great, easy exercise. One of my favorites, as
it involves zero cardio. So what you do is you just
stand in a serving position, and you toss the ball up, and you make sure it always
lands in the same line as your arm. So your arm is straight
as you toss it up. And repeat 50 times.