Things can get tricky when you are renting a room from a friend who you are also living with. The Move Channel.com has some things to consider before deciding to take the plunge with friends.
Make sure to set basic ground rules and that you are clear on how your roommate/landlord wants the property treated. Also consider that if you live with a friend and you have friends in common, you may wind up socializing with the same people all the time.
Decide how bills will be paid and split. You can call your utility company to get an estimate for how much bills will be. Be respectful of your friend and pay your rent on time. They may be a little more forgiving if you're late, but don't sour your relationship by by chronically turning your check in past the due date.
If your landlord is a couple, make sure you have a contingency plan in case they break up. Also, stay out of any arguments they may have and don't take sides.
Finally, if you are renting from a friend, you may not have a formal lease contract to sign. Cover any questions you have and perhaps write them down and sign it so both parties are on the same page.