my friend that can land backrolls says that he first learned to do it on a tramp and that it really helped should i learn how to do it on a tramp before i try it on the water

it gets you used to flipping. Make sure you hold on with both hands and do a sideflip. Dont let go and do a frontflip (trampoline frontflip) with only one hand on the handle.

i could do back rolls before i could do sideway spins on the tramp. the way you throw this trick on the water is different than on a tramp. also i always come straigt down on the tramp which has given me that bad happen on the water. so now instead of leaning back a little i clip my front edge and hit face first.