After an employment interview, writing a thank you letter or e-mail is a must. In fact, some employers think less of those interviewees who fail to follow-up promptly. Plan to send out your thank you letters as soon as possible (preferably within twenty-four hours) after your interview.
Like any piece of writing, it is best to keep your audience in mind. Address their issues and concerns. Consider the "personality" of the organization and the rapport you felt during your interview. In addition to thanking the person you talked with, the thank you letter reinforces the fact that you want the job.