Lower your trophy pose right hand. That allows you to finish your swing as you're hitting the ball, anything beyond is only to slow down and prep for the next shot.
Arch you body like a bow that is drawn, something some pros barely do.
After ball contact, your elbow and hand should be at head height or higher, while the racket is pointing straight down at the ground.
You have to slow down to preload your serves. THEN explode up and towards your opponent, around a 45 degree upward angle.
Watch Hewitt and Ferrero serves.