I remember my choir teacher in high school told me, 'When in doubt, sing loud.' I'm a terrible singer, but I always auditioned for the musicals, and would get cast in them because I really would just put it all out there. That was really good advice, and I think it works for everything, not just acting.
Ethical decisions ensure that everyone's best interests are protected. When in doubt, don't.
When in doubt, make a fool of yourself. There is a microscopically thin line between being brilliantly creative and acting like the most gigantic idiot on earth. So what the hell, leap.
When in doubt, always opt for going naturel rather than hiding your skin under foundation and such. Line your eyes with kohl and mascara, put on some bright lip gloss and pinch your cheeks a little bit to get them all flushed and bright!
When in doubt, take more time.