You'll need to do some uphill running intervals in your off-road cycling shoes, as well, starting easier at first and then working up to speed, focusing on making the most of the traction your cleats offer on steep, loose terrain. Try them without carrying the bike at first, later adding the extra weight and burden of the bike on your shoulder.
Speaking of that bike on your shoulder, don't underestimate the cost of the motion to lift and carry your bike. Bring your core strength up to par with abdominal and back work, and again start slowly with your dismounts and remounts. You should have at least four to five sessions of running under your belt before attempting dismounts and re-mounts. Practice them at low speed during base-training sessions until proficiency is achieved.
One suggestion: take a skills clinic regardless of your experience. A few afternoons spent polishing your dismounts and remounts can help save precious seconds in races later on. Plus, 'cross clinics are just plain fun. When did you last run around kicking up leaves in a park or schoolyard as an adult?
One frequently asked question is if a rider should lift weights as part of their winter training while they race 'cross. If you have performance expectations even while "training through" your 'cross season, I suggest that lower-body strength exercises are done on the bike.
Meanwhile, upper-body exercises are encouraged during 'cross season, particularly for women and anyone who may be lacking upper-body strength. You'll lift your bike a minimum of 12 times in a typical race. The less it "costs" to lift the bike each time, the more energy you'll conserve.
Sadly, the 'cross season eventually comes to an end. The nice thing about the timing of this end is that it coincides with a time of year that's usually difficult for training for most, with the holidays, school finals and the "end-of-year" rush for many businesses—a perfect time for a real end-of-season break.
For instance, if you're a student and you take a break from mid-December (the day after nationals for most U.S. riders) through at least December 26th, you'd still have more than a week of holiday break to jumpstart next season's training.
Still, should you ride two seasons year after year? The answer depends on the relative importance to you of each season. The deeper your category's field, the more difficult it is to excel in a two-season year, and you may have to choose one over the other.
Even pros may have several years where they have both an excellent mountain bike and 'cross season, but when it becomes an Olympic year, you'll see them focusing solely on a single discipline. If your goals are lighter hearted, celebrate the availability of bike racing all the way into December by making the most of it.