I took my state board exams in North Carolina, so I can't speak for California specifically, but these are my tips:
1. REMEMBER YOUR SANITATION! It is extremely important, and could mean the difference between passing and failing if you forget to sanitize your hands, close the trash bag, dispose of things properly, etc.
2. Remember what is required of you. It is all in the Candidate Information Bulletin. You are being tested on the items listed there. Nothing more, nothing less.
3. Do your best. Do as you were taught. If you see another candidate doing something differently, don't panic. Do as your instructors taught you to do.
4. Don't panic if you don't finish a procedure.
5. Check your kit bag, and then check it again.
6. Keep your kit bag CLOSED when you're not taking something out of it, or putting something into it.
7. Listen to their instructions. Follow them to the letter. If they instruct you to stop, stop immediately.
8. If you fail...you fail. It happens. You just have to try again.
9. On the written examination, if you don't know the answer to a question, make an educated guess. Try to find something in common between some of the answers, and use that to help you. The answer may even be in the question itself.
Good luck! If you have any specific questions, feel free to message me.