Round Up Your Contacts
Make sure none of your interviewers' business cards fell out of your folder on your way home. If you're missing any, call the company's reception desk and ask for the email addresses and phone numbers that you need.
Jog Your Memory
Under each of your interviewers' names, write notes about the things you learned from your conversations with them. For example, if you discussed your interest in books and an interviewer recommended one for you to read, make a note of it to use in later communication.
Send personalized thank-you notes to each person who interviewed you, and mail them no later than the following morning. An emailed note is sometimes appropriate, but a hand-written note is a bit more memorable. Giving a genuine note of thanks will make it obvious that you are taking the opportunity seriously.
Critique Your Performance
Review your interview experience so you can learn as much as possible for the next time. Jot down questions that were asked, answers you wish you had given, and give yourself an overall performance evaluation. Don't beat yourself up if it wasn't your best, and stay positive that you'll get better with every interview.
If you haven't heard from the employer within the time they expected to make a decision, email your contact to see where they are in the process of filling the desired position. Make it short and sweet, reinforce your continued interest in the job, and sign off with sincerity.