An optimal tennis serve toss is when you can serve flat, slice and topspin serves with comfort and power. This video shows you a comparison of different ball tosses for different serves. The toss for a flat serve is basically the same as the toss for the slice serve - the main difference is how you hit the ball. You simply hit it more from the side when serving slice. The toss for the topspin tennis serve is more behind the back but still inside the court. You still need to lean into the court to generate power for the kick serve although your main momentum needs to be upwards in order to generate a lot of spin.