For your Personal Use:
Thank you letters are the mark of a socially skilled person. Taking the time to write a brief note of appreciation for your interviewer's time will make them glad they took the time to meet you. It will also leave a favorable, lasting impression. The elements of a thank you letter are:
Statement of Appreciation:
Thank them for their time.
Restate Discussion Point:
Include reference to at least one topic of discussion during your visit.
Match for Job:
State that your qualifications will meet the needs of their company. Let them know you are interested in the job.
Next Step:
State that you will contact them in the near future.