Don't go alone This is the first and most inviolable law for any off-trail skiing. Bring a buddy, and advise others of your itinerary and time of return.
Dress properly Wear or bring several layers no matter what the weather report. Wear a synthetic fiber next to the skin, Gore-Tex or a similar waterproof/breathable fabric on the outside, fleece or wool layers in between, and bring an extra layer in the pack. Cotton is not acceptable. Layering enables you to manage heat at different levels of exertion and in changing weather.
Wear a pack You're going to need it to stow your skins, Trekkers and that extra layer. Pack food and water, waterproof matches, extra gloves and a compass. Bring the cell phone, if you have one, but don't rely on it.
Respect your skiing ability Before setting out, make sure you can ski effectively in any type of snow. If you're lucky, it'll be waist-deep fluff. But it might also be frozen crud bearing the fossilized tracks of previous adventurers. Backcountry skiers learn to love it all. Before you set out, practice inbounds. Dip into the woods between trails and seek out difficult conditions until you're sure you can master whatever nature presents.
Know the territory and what to expect That means acquiring the appropriate topographic map, learning how to read it and plotting a route prior to setting off. How long is the trek to your destination? How steep are the pitches you'll climb? Are there trail markers?
Finally, get an early start First-timers often underestimate the long slog back to civilization, only to run out of steam or daylight before the round-trip is completed.