I am trying out for cheerleading next fall and I will take any suggestions and they don't necessarily have to be about jumps. It could be tumbling, movements, anything!
I would definitely start lifting for your tumbling especially in your legs and shoulders.
Squats, push ups, and any type of ab work will help.
Also try sitting down with your legs out as if you were about to street, with one arm in front of you and one arm behind you, lift one leg at a time and rotate it in circles - it really helps!
Stretch a lot!
The best thing I can say for your motions is practice them in front of a mirror!