Here are a few basic tips that I found helped me:
1) Stretch and exercise your legs, back, shoulders and neck regularly - this helps when you're on the mountain. Using your own body weight for squats, etc helps a lot...no need for heavy weight lifting. Throw in some cardio so you don't tire as easily at altitude. Getting sore and tired is main reason people crash.
2) Relax your shoulders...don't tense up.
3) Maintain good posture - when you are new there is a tendency to bend over forward at the waist, which throws off your balance. Push out your belly button and pull in the small of your back to keep good posture. If you get tired...take a break until this feels natural.
4) In the beginning, keep your eyes focused ahead and where you want to go. Don't look at your feet to see if you are engaging your edge...you will fall. Keep your head up and ride in a confident posture.
5) Make sure you always have 51% of your weight on your front foot - don't ride on your back foot.
6) Put pressure on the tongue of your boot to engage your toe-side turns.
7) Check to make sure your bindings are set up properly (no toe or heel drag). Lace up your boots without your feet in them and place them in your bindings. Ratchet your bindings on them and look to make sure they are centered on your board without too much overhang on either side.
Most importantly, get a lesson! The instructor will be able to help you with all of this a lot faster than you can figure out on your own.