The service toss yips are very frustrating and hard cure, mainly because the problem is usually mental. If you toss the ball fine when you're practicing or playing for fun, but have problems when the pressure is on, you've got the yips.
As far as the mechanics of the toss, keep these points in mind.
keep your tossing arm straight
hold the ball with your finger tips
don't flick your wrist, the only joint in motion should be your shoulder
That's it for the mechanics. Now for the mental issues. Try the following.
relax, catch any bad tosses and remember, it's just tennis
visualize tossing the ball straight up a chimney
if the toss problems continue resolve not to let it affect the rest of your game
Above all else, have fun out there and enjoy the process not just the outcome.
