Laugh at yourself, but don't ever aim your doubt at yourself. Be bold. When you embark for strange places, don't leave any of yourself safely on shore. Have the nerve to go into unexplored territory.
I'm probably one of the worst actors as far as preparation goes, because I actually don't prepare. I find it easier to read the script and whatever hits me in my stomach, like deep down, I just go with it. And the director kind of molds me whether to go right or left with it.