Ball spins when tossed up - gripped too hard, try to hold loosely in your fingers
Ball toss going behind - cocking wrist towards body, try to cock wrist towards net
Ball coming into you - letting go with bent arm causing ball to come into you
Letting go too early - see it as a placement and let go around shoulder height
General inconsistency - smooth action to place in air, no jerky movements
No target for ball toss - try to work out ideal placement (height/direction) for your ball toss before starting your service action