You probably know this (hopefully) and you hopefully already do it (probably) but, if not, this is something you need to know and do.
If you interview at an agency, write thank-you notes to everyone who interviewed you.
Just a simple card or email (cards are nicer, emails work) that thanks them for taking the time. Maybe you mention something you talked about. It goes a long way, and it reminds them of you.
This means that when you interview with people, you might ask if you can have a business card or at least write down their name (spelled correctly).