Start off by practicing some ollies off of flat ground. This will help you adjust to being able to jump and pull off some height when you do jump with your snowboard. After practicing how to ollie off of flat ground, get a feel of the ramp and learn how to do a simple ollie off of it. It is going to be the same as when you do it on flat ground, only you will have to time it so that you get maximum height, by pulling of the ollie at the ideal time.
Now after you have done all of those practice runs, go on and set yourself up to hit the ramp by building some speed and heading for it.
Just as you are about to reach the ramp, start to lean a little backwards. This will help you generate the turning momentum when you end up making the jump.
As you hit the lip of the jump/ ramp go on and throw yourself forward. Spring as far ahead as you can, however, keep your shoulders in place and keep your legs tucked in as well.
Now follow through with the movement of the front flip and try to finish so that you land on your board after completing a flip. Chances are that you will end up messing up the flip the first few times. This is why you should start off with smaller jumps, while slowly moving towards the much harder ones.
You need to remember that the key to pulling this off successfully is to practice it quite a few times. You are bound to end up failing the first few times, however, once you get the hang of it you will be pulling off front flips with no problems at all.