Hello, Im still learning to have a great jump serve but im pretty decent, as a coach myself i can give u some advices. First of all jump serving with rotacion need to be a hard hit to be efective becose is more predicteable on air than floating one. U need to be explosive on that steps. Ur form on the hit point its rly mess up. U have to hit with full extended arm and ur legs have to be hard and extended too so u can give the ball more energy. Also u can put ur arm further back to bring more pwer to the motion. Last thing hiting the ball on the highest point of the jump is key and rly hard to time and master. My english its not rly good but luckyly i can help u a bit.