I found this article on CNET's News.com for businesses concerned about their online reputations. I'm adapting the tips for teens (and their parents). Here goes...

Prevention is always best.

- Always strive to view anything you put online under your name through the eyes of not only your friends, but any adult (potential employer, grandma, teachers, etc.) who may "stumble upon it"

- Create a public blog, profile or portfolio site that always puts your best foot forward, leave thoughtful comments on other people's blogs under your name. The more positive public content you put out there under your name the higher it will rank in Google search results (pushing down the not-so-positive stuff you can't get rid of)

- If you do see something negative posted about you without your permission, try to have the site or person delete it or take it down.

- If there are photos of yourself you wouldn't want copied and pasted anywhere else online, remove them from your profile or ask your friends to remove them.

Keep tabs on your virtual identity

- Use Google and Yahoo email alerts for your name, as well as "Googling" yourself in all major search engines regularly

- Also keep an eye on the blogosphere -- using sites like Technorati to search under your name or blog URL (Technorati now indexes MySpace blogs). You should also regularly monitor your Facebook Newsfeed and check to see if anyone has mentioned you or tagged you in a photo you don't know about.

And...

- Decide whether a response or discussions are better suited for offline, one-to-one conversations

- Take time before responding to remove any chance of emotions tainting your response (that you might regret later)

- If you're responding to something that has pissed you off, have a friend read it first (whether it's a comment, email, IM or any digital form of communications)

- Remember that what you say privately could be made public by others

- People have always been able to say negative things about you; now it is just easier to do it publicly, but it is also easier for you to counter this with positive information you can post about yourself.