It's easy. Go buy a new mountain bike and ride it. First creek crossing you come to, just go for it, never mind whether you know how steep the little channel you have to cross is or how soft the gravel bottom is.
I've been thinking about a mountain bike for a while now, I'm very close to some of the best trails in the state. Plus I want something to ride on gravel and around dog trials. I'm a good sized fellow thus the decision to go with a 29'er, mine is the 21.5" frame size. It fits nice after changing out the stem for one that is a bit shorter and with about 30 degrees of rise.
Even though my back is a bit sore today from yesterday's tumble, I'm sure this bike will be a lot of fun and let me go more places than ever.