After the InterviewBack in Touch - Ask the interviewer when s/he expects to get back to you on her/his decision.
Get Everyone's Business Card - Before you leave, be sure to get the business cards of all of the people with whom you visited. If you cannot do that, ask a secretary for their names and e-mail addresses.
Thank the Interviewer - Verbally thank the interviewer for taking the time to interview you, before leaving. Within a day, send thank-you letters to all of the interviewers with whom you spoke. This does not need to consist of a written letter sent via snail mail; an e-mailed thank-you works just as well.
Do not give up - Sometimes, within ten minutes of the start of an interview, you will know that the job is not one you want to pursue. If you begin to feel this way, don't give up on the interview. Continue to interview as if the job was the most important thing in the world. This provides you with practice for your next interview, which may be for your dream job! Not all interviews will lead to offers of employment, but, if you approach every interview as if it's the most important interview you ever had, you will come out a winner!