The following is reposted from an earlier thread on tossing:
http://tt.tennis-warehouse.com/showthread.php?t=418152
The last part specifically tells how to toss further into the court for a first serve, but the intro tells how to have a consistent serve.
Check out the sequence of Sampras tossing below:
Like all the pros, he tosses with his arm parallel to the baseline.
Federer Murray Haas & more ball toss common threads:
http://www.youtube.com/watch?v=lIF-UaRUd6k&feature=related
(The reason for this is so as the tossing arm goes up, your shoulders can be well coiled by ball release (pic 7), so you don't feel rushed getting into a trophy pose before having to start the racquet drop/swing portion of the serve.)
As Pete demonstrates above, the arm is kept straight with no elbow or wrist bend. (So the arm moves only at the shoulder.)
The ball is simply released when the hand reaches a point a little above the shoulder, at eye level:
By having kept the arm straight with no wrist or elbow flick, but merely opening the hand to release the ball, the ball will go up and come down in a parabolic shape that resembles an upside down J (hence why they call the toss the "J" toss):
As long as you bring the arm up at the same speed, follow the same path up with your arm, and release the ball at the same point, it should always go in the same place.
If you want the ball to go higher, bring it up a little faster.
If you want the ball to drop more past your body to the left, release it a little later.
If you want the ball to drop more to the right, before it reaches your body, release a little earlier.
(Reverse these directions if you are left handed.)
Now for the trickier part, how to toss more into the court, or back more/over your head:
If you want to toss the ball out into the court for a first serve like Sampras does above, start the toss with your arm closer to your back foot (pic 1), and as you bring the arm up, move your arm ever so slightly forward so that by the time of release, your arm is past your front foot (pic 7). [Note that at about half way through the toss in pic 3 the ball has been moved forward to a position 1/2 way between the front and back foot.]
(And obviously if you wanted to toss a second serve to land directly over your head, just start bringing your hand up with the ball in between your feet (like the position the ball is in pic 3, but starting with your hand lower) and just bring it straight up between your feet.
Hopefully, I've given you a way to help solve your serving woes.
Oh, .... but one more thing. Even if you understand what to do, it will still take practice to really get it down.