Do: Talk about your life outside of advertising. If you don't have one, make something up. Those people on Friends have interesting lives; try using one of their storylines.
Do: Make personal contact with the recruiter or CD you are leaving your book with. They probably won't hire you based on your looks alone, but at least they'll know you're not a drooling idiot.
Do: Have a question ready for the end of the interview, preferably one that demonstrates you've been awake for the past 45 minutes.
Do: Write a thank-you note. Here's your chance to remind them of that dashing wit.
Don't: Talk about just one account you want to work on. You're a team player, remember?
Don't: Put down your own work too much. They'll know it sucks without your pointing it out.
Don't: Wear a lot of perfume or cologne. It's a job interview, not a dance club in Jersey.
Don't: Speak badly about your former employers. Do unto others yada yada yada. The point is, it makes you look good to speak well of your old bosses, you old brownnose you.