1) Google yourself. While this may seem like a vain pursuit, you need to see what is out there. If you don't like what you see, you need to create some positive search results. Writing an article for an online paper, having something written about you or posting to a blog with your name can all help. Make sure that what is reflected in these new results is applicable to who you are. For example, if you are passionate about the environment, post to a conservation blog or an article that references this subject.
2) Fix your image. To create a positive image and share the other side of who you are, swap out some of the snapshots of in front of cool cars with the time you spent travelling abroad or volunteering with local schools. These images can leave a lasting impression on admissions officers.
3) Be professional. We all want to switch into informal language when using online communications. Make sure you always capitalize and punctuate as appropriate and sign each email with a formal name. Another easy step is to develop a email address that isn't partyguy2012. A simple firstname.lastname@example.org should suffice.