You have spent hours writing, rewriting and proofreading your resume. Your cover letter was perfectly tailored to the company's needs and wants. You poured over interview questions for days rehearsing just how you would approach each one. You got an interview and nailed it. However, as you left the interview room you noticed the line of other applicants waiting to interview for this position.
They likely spent just as much time prepping for this as you did. How can you make yourself stand out? Often the best route is simply to remind the hiring committee of your name. After a long day of interviewing sometimes names faces and credentials can blur together. A quick reminder could be just the thing. That is where the post-interview thank you letter comes in.
You need to be sure that your post-interview thank you letter follows standard letter format. With the proliferation of templates (Microsoft Word has great ones) this should be the easiest step. Find a business letter template and follow it. Hopefully you already did this with your cover letter. Then you can simply follow the same format.
Next, reintroduce yourself and what you applied for. Don't assume that because you remember them, that they remember you. Gently remind them of the credentials you showcased during your interview.
At some point either in the interview or as part of your portfolio you should have stated the type of job you wanted and the type of firm you would like to work for. Tell them that the interview showed you how good a fit you are for each other. This is a good way to restate a lot of your skills and abilities without sounding repetitive.
Now, recall a comment or some dialogue that occurred during the interview. Maybe you went to college at the Alma mater of one of the committee members, or maybe you mentioned in passing you were a passable softball player and would love to play on the company team. Say something that is positive yet casual. The hiring process is as much about getting someone to like you as it is showing off your abilities.