I'm still saying that "exercising" isn't essential. I'm only saying this because I have many friends that can hardly run down their driveway, but are great snowboarders. I can't speak from personal experience, because I run 6 minute miles and am in shape, but just thought it was worth mentioning.
I'd say as far as physically preparing yourself for it, STRETCH!!! Stretch for at least 5 mins, ideally 10 before you go out. You will be bending, falling, faceplanting, landing on your wrists, etc. more than you probably ever have in one day. If you're not well stretched, you WILL do harm to your body. Whether it be just a minor hyper extension or even a pulled ligament, stretching is your best defense to injuring yourself.
As others have said, do make an effort to put forward weight on the board. It's much like learning to drive a car. At first, it seems there's so much to think about, you'll never get it. But eventually your body will learn the movements subconsciously and snowboarding will just flow out of you, instead of thinking about it. For example, instead of just saying, "Let's cut off the groom and go in that little tree trail and come back out," at first you'll be thinking, "Ok, lean forward, dig my heels in, balance the board so I don't catch an edge, now hold this balance till I turn into the trees, then switch edges very carefully, then dig my toes in, balance, and come out!"
The biggest thing about snowboarding is just doing the movements over and over until you have enough confidence/muscle memory to do them without even thinking about it. Just remember, don't get frustrated if you don't get it at first, no one does. Stay confident and practice good form.
