To protect yourself from premature character assassination, follow this rule:
Never post anything online that you wouldn't want your grandmother to see.
This means you need to "un-tag" yourself from those high school and college party pictures and any movies posted on YouTube from road trips with your friends. Another potential pitfall is being part of off-color, sarcastic jokes. While you may see them as harmless, a parent may not, and instead see them as offensive. These could appear in wall posts or tagged photos. Remember, once your image is tarnished, you may never be able to get it back.