Well, this is my tip of the day Do your rocking motion/weight transfer, and hit UP on your serve, don't try to send the ball on a straight-line trajectory ending at the target point (should you do that, it will, most of the time, end up in the net), but try to aim at contact towards a point higher than that on the same vertical. The ball will curve down under gravity, the lashing effect of the arm (simultaneous with the forearm pronation), and as a result of the spin which you need to impart for control purposes. Your knee bend and your hip rotation should help with that. Especially effective on the kick serve. Your ball trajectory will be higher, and it will also kick higher after impact. Comments welcome, of course.