Tossing the ball accurately and in a relaxed fashion are two essentials when it comes to the serve. To accomplish both, practice tossing the ball so that after it leaves your hand it carries to the spot where you’ll hit it without any spin. First of all, make sure you hold the ball on the pads of the fingers. Before you start the windup your tossing hand should face the side fence, not straight up. Release the ball somewhere between eye level and just above your head and gently spread your fingers open as you let go of the ball and continue to move your arm into a 12 o’clock position. (Picture the pedals of a flower opening in time-lapse photography). This accomplishes two things: 1., It allows you to lift and “place” the ball which is more difficult if you snap your fingers back on release and 2., it immediately sets the tone for staying relaxed through the stroke.
Watch the service tosses of the truly great servers (Sampras, Federer, etc.) either on television replays or in the Pro Strokes section of Tennisplayer.net and note the repeated use of the things I mentioned above. Once you get the hang of it it will set a very positive precedent for successful serving.