Show what you know.
Don’t invent new math.
Don’t contradict yourself.
Do the easy questions first.
If you don’t know how to do a problem, start by writing down relevant things that you know are true in general.
Break difficult problems into manageable pieces.
Know what a function is, and know what things are functions.
If you aren’t taking a derivative, it’s probably wrong. (see the explanation below)
If you’re doing obscene amounts of computation, it’s probably wrong.
Don’t care about the final answer.