It all starts with your Facebook page. You've probably already heard people say that you need to remove inappropriate photos from your profile, but that's only the start. Go through all of your comments and delete any that contain profanity or anything else that can be construed as offensive. This also applies to what you list as your interests, favorite movies, etc. Finally, you should change your privacy settings so that only your friends can view your wall. This is a necessity if you have friends who tend to be inappropriate with their postings.
The next thing that you need to change is your voice mail. Your friends probably think your outgoing message is hilarious, but employers won't be amused. You shouldn't give the caller any reason to hang up, so make sure to use a standard greeting.
A similar rule applies to your e-mail address. It's a good idea to create a new account for your job search activities. Not only will you avoid having to apply to a job with a less than professional account name, you will also spare yourself the work of having to separate personal e-mails from job search ones.
People today are used to being able to answer calls or text messages while doing work, but this is not appropriate when you are in the middle of a job interview. To avoid any potential distractions, you should completely turn off your cell phone. Leaving it on vibrate is not an option, as you will still be aware when you are getting a call or a text. It's better to not know when you are being contacted when you are trying to answer important questions.