A thank you letter should be laid out in the following format.
Mailing address of the receiver: Type the Name, Designation, Company Name and Address on the left top corner of the letter.
Greet the receiver: Before you start off with the letter greet the receiver of the same as ‘Dear’ while addressing him or her as Mr. or Mrs. or Ms. whichever is appropriate.
Starting paragraph: Here you should thank the receiver of the letter and mention your reason for the gratitude.
Body: The body of the letter must contain two paragraphs with details of the meeting or the occasion that transpired into a letter of gratitude towards the intended person.
Last paragraph: In this short paragraph thank the receiver all over again and wish him/her in the most appropriate way.
Closing: Close the letter by signing off “Yours Sincerely” and then write your name and sign below that. Mention your designation and company name here as well followed by your mailing address.