It's that time of year again. The 22nd annual Rubithon run is coming. Make sure to checkout the Rubithon website for more information and get registered.
Hollister would be a start, but you need to get on some rocks to build your skills and see if you even like doing it. As soon as the snow melts you should hit some trails in the Sierra Nevada.
Keep an eye on the trail planner for some of the summer weekend runs like, Slickrock to get some experience playing on the rocks. They are not as intense as Rubicon and body damage is less likely.