The rules to follow up after an interview are simple.  First, you must do it and second, you must do it correctly.  If you don't follow up, you risk presenting yourself as uninterested in the opportunity or rude.  You want to show that you are courteous, attentive and a good communicator.  After an interview,  remember to:1.  Write a thank you note immediately after the interview.  Within 24 hours (and the sooner the better), send an email to everyone that you met.  If you want to send a handwritten note, you can also do that but, today, most hiring managers accept email thank you's.   Not every interviewer will give you a card, so you can call and ask for the email address or send a note via snail mail.2.  If interested in the opportunity, let the interviewer know.  Give them your honest feedback.  If it's not right for you, let them know.  You want to keep the door open for other opportunities.3.  Find out the next steps.  Before leaving the interview, you should ask about next steps.  If the information wasn't given, you can ask in your note.  Be prepared to wait as they may still be interviewing.4.  Know who is in charge.  If you are working with an outside recruiter, this person will be your contact and all follow up should be done through their office. The same is true if your are dealing with an internal recruiter or HR department.  Unless you are specifically told to contact an interviewer, don't bother them.  You might think you are being proactive but they may think you are being aggressive and annoying.Best impressions count!