As far as thank you letter format is concerned, you can keep it simple. But don't just send a short email that says: "Thanks for the interview. I appreciate the time you took to interview me. I am very interested in working for you and look forward to hearing from you about this position." You'll still stand out from other candidates, even with this short note, but you're losing a prime opportunity to boost your chance of getting a job. A longer email allows you to point out a key substantial item or two in your favor.
Always begin with the pleasantries: mention how you enjoyed talking to them, additional thoughts about how you and your skills are a great fit, and what you learned from the interview that makes you even more enthusiastic about working for the company. Be specific.
Send a thank you note even if the job interview didn't go so well. The thank you note provides the perfect opportunity for damage control. Don't write a book, but feel free to address issues like misconceptions and things you forgot.
Be sure to send a personalized note to everyone you spoke with about the job. For example, if you were interviewed by a panel, make sure you send a message to each person on the panel.
Here's an example of an effective thank you letter format.
Dear Mr. Manager:
Thank you for meeting with me today to discuss the _____ position. I'm now even more enthusiastic about the prospect of working with you at [the company name]. I am more convinced than ever that my skills in [succinctly insert a few skills here] are a strong match for what you need to accomplish the challenges and issues we discussed. [You can mention specific challenges here.]
I also believe that my experience is A, B and C would bring an additional advantage to solving these challenges and providing solutions. I am really looking forward to discussing this with you again. I'll call you on Friday to discuss setting up the next step.
Don't forget: The most successful job-seekers send a thank you letter soon after a job interview-within 24 hours. To get it there that fast, you have to send it by email.
If you can send a strong thank you note like this within a day of your interview, you will be making the smartest follow up move you can make.