Stanford. They don't call it the "Harvard of the West" for nothing. Even if they don't call it that.
UC Berkeley is up there as well, perhaps the best public university in the United States, and UCLA is aight. Really, all of the UCs are good. You can never go wrong with them.
For private schools there's Caltech, if you're into STEM, USC is decent too (contrary to popular belief that it's just about $), and then you're left with LACs, which CA has no shortage of. Try Pomona, Claremont McKenna, Harvey Mudd, or whatever.
(there are a ton of other great colleges in CA; just going off rankings here)
To get into any of those schools is the same as any other top college in the US. Get a high GPA, high SAT score, good ECs (and be especially involved with a few of them), etc.