The most important thing in riding cyclocross is maintaining speed. Because cross courses are usually chalk full of hills, mud, sand barriers, steps, and various other obstacles you are going to really need to learn how to keep your speed despite facing them.
If you're riding cross, the single most important skill is learning how to get off and run with your bike, then get back on again. Maintaing speed while doing this is only achieved with practice. Here are some tips on how to learn!