It's mostly about developing your reflex-to-control abilities. You should be constantly scanning in front of you and picking your next line; visualize what your gonna do in your head rather then reacting when it comes up. To ride trees fast and efficiently you need to be making decisions about your line every 1/2-second a new "frame" comes into view. Right now since it's new your likely uncomfortable having to make split-decisions and commit to them, so instead your bailing out every time. Like anything it's something that just comes with time and practice, once you get over the fear of hitting trees it will all just click.
Once you get it down, it's easily one of the funnest and most intense things to ride. Snow is a big factor too... if you have ice-burms and hard conditions they're hard to ride no matter what. Deep powder also tends to suck since it drastically slows down your turning speed. 4-inches to 2-feet tends to be the best.
PowderHound and TreeNinja