Some things I've learned:

Helmet.

Learn to strap in standing up. Easiest way is to place your board perpendicular to the fall line, dig your heel in to chop out a platform, then balance there while strapping in. I can strap in much faster this way and never get my butt wet.

Did I mention to get a helmet?

Keep your chest pointed towards the tip of your board while riding. This drives good position when turning and carving. You should be slightly crouched, knees bent and hands forward for balance, a little wider than shoulder width apart. Like you have your hands on a counter. I find positive angle stances help me keep this position, about 24 front and 12 back.

Red makes some good helmets.

Learn how to carve, not turn (sliding), carve. This is where the tail of your board will follow in the same track as the tip of your board, creating a trench for skiiers to fall in (I used to ski too). This increases the fun factor by 2x-3x. I could spend all day at the park, or carving the groomers - either way I'd have a good time. Bomberonline.com has some good articles on learning to carve.

Helmets are useful if you run into something, but also work when someone runs into you.

Have fun! Snowboarding is about finding your own style, I have a ton of fun exploring the sides of trails for small banks, jumps, bits of powder, etc. There's always a way to have a good time with a snowboard, especially if you're riding with a bunch of friends.

A helmet bit my sister once. No realli!