There are two simple steps you can take to make a lasting impression after your interview and greatly increase your odds of success.
The first is to call the interviewer to thank them for their time. If possible, you may want to add additional information which was not discussed in the interview. An example would be: "I understand from speaking with the receptionist that Microsoft Office is your corporate software standard. I just wanted to mention that I'm also fully proficient in each of the tools in the Office suite." This phone call should ideally take place the same day. If you are unable to reach the interviewer directly, leave a voicemail message.
The second activity is to immediately write the interviewer a short note, thanking them for their time and re-emphasizing your interest in the position. Then do your best to get it to them as quickly as possible. E-mail it, fax it, hand-deliver it, messenger it, use overnight mail, whatever. But be sure they have it before the end of the following day. Ideally, you want to get it in their hands by the end of the day of the interview or first thing the following morning. Why? Because the quicker your letter arrives, the greater the likelihood of effecting a positive outcome. Doesn't everyone follow up like this? Hardly. Virtually no one calls after an interview and only a few take the time to write a personalized "thank you" letter. The simple gestures of a phone call and "thank you" letter can make a big difference in separating you from your competition.
A "thank you" may seem obvious, but I can assure you that the majority of students do take time to say "thanks."
And if you interviewed with multiple individuals, make sure each "thank you" letter is unique. Common language is acceptable, but do not simply change the name at the top of the letter. Your application, resume, and other materials will likely be stored in a single file, usually in the possession of the person guiding you through the hiring process. Your "thank you" letters will eventually find their way back to this central file. Yes, we do compare notes. And what seemed to be a unique and original note can lose its impact if there are two or three duplicates collected together in your file. It has taken a great deal of effort to get this far. Take the extra time to make this final impression a positive one.