Backs
A back flip is one of the easiest tricks to do (If you are naturally a flipper, some people spin better), but one of the scariest to learn. If you have them solid on the tramp, you can do them on the snow. Just be sure to pop and not chicken out. It also helps if the jump is more of a kicker. It will give you more rotation and will hurt less if you come up short. Also, try it off a small-medium sized jump your first time. You don't want to go huge and die. As you pop off the lip on your first try, set your rotation by throwing your arms up and your head back. If you're on a small jump, try to remember to tuck it up too, as that will help you rotate faster. Then just spot your landing and put your gear down. As you get better you can start stalling them and adding grabs. However, for your first one you just want to be sure and get around. Hope that helps and good luck.
Fronts
Fronts are harder because they are blind most of the way. Be sure and wait for your pop and don't throw the flip early. As you pop, throw both arms down and tuck in to a ball. Then just stay tucked till you see your landing. I actually like a little pop on the jump to help set the rotation. Personal preference.