In the past, I've done almost nothing to prepare, and I've got the results to prove it. Mostly, I just rode lots.
Last year, I went to a series of clinics at Alpenrose. That was very helpful and I came out able to cruise the barriers and shoulder my bike like nobody's business. Unfortunately, my physical conditioning was more than enough to keep me at the back of the pack.
This year, I have every intention of being more serious about training. I'm doing weight lifting and running right now to increase power and build my aerobic base. Toward summer I plan to spend some time working on my bike handling skills and doing some focused workouts to boost my anaerobic endurance. As 'cross season approaches, I want to work on sprinting while carrying the bike and running up hills, and I'll definitely be going to the Alpenrose clinics again.