What you should ask for depends on your individual situation and what you bring to the table. If you are a valuable member of the team with a lot of experience, you should expect to be handsomely compensated. If you are just starting out, you should expect to be paid fairly, but not as much as someone with more experience.
In general, you should try to negotiate for the following:
-A competitive salary
-A good benefits package
-ARelocation bonus (if you're moving to Silicon Valley)
For more specific advice, I recommend you check out this article: