Deffinetly make sure you air down.The wider your footprint the more traction you'll have.Snow is sometimes worse than mud,it can get really slippery.Keep your tranny in 4-lo and let your motor do most of the work rather than your brakes,especially going down hills..
Another thing is to check out the area your wheelin' in.Reason being is that the snow covers alot(rocks,ruts,sticks and so on).Have a shovel handy in case you have to dig yourself out.Never travel alone.Bring an extra pair of shoes & socks(in case you have to get yourself un-stuck and your shoes & socks get soaked).Also if you get yourself stuck pretty decent use stuff like tree branches and rocks and put them around tires to gain traction..

But wheelin' in the snow isn't all that bad as long as you keep in mind some of the things that I mentioned.I personally love it.It makes all the trails that your used too challenging all over again...