I have been trying lately to help folk with their service, and one big point I try to make is with the ball toss.

The non racket arm when it releases the ball should be parallel with the baseline, as shown in this great video that I found on You Tube.

By releasing the ball in this way, the shoulders and the hips rotate more(the body acts like a coil)and the shoulders move correctly.
Also with the toss of the ball more above you, you can develop with practice an upwards serving motion.

If the ball is tossed, or placed, out in front of you the shoulders do not work, or the hips and the action becmes more of a push.
Yes you can get the ball in, but with no real pace and also no spin, whereas if you spend alot of time practicing this upwards hitting motion you can develop spin.