Open up your computer's word processing software to a new document. Type the current date on the first line of the page, left-justified, and then enter down two lines and type the first and last name of the recipient. Enter down one line and type the street address of where you will send the letter, and then enter down one more line and type the city, state and zip code of the address.
Enter down two lines to write your salutation. Type "Dear" and then either address the person informally using the first name (i.e., "Dear Sean") or formally using the last name (i.e., "Dear Mr. Reynolds"). Whether you address the person informally or formally depends on your relationship with that person and how he or she prefers to be addressed. When in doubt, it's better to address the person formally rather than informally.
Enter down two lines and write the body of your thank-you letter. Explicitly thank the person for taking time to meet you or to talk over the phone. Express how honored you are and that you are looking forward to working with the person again in the future. If you are attempting to strike a business deal, remind the recipient of some of the strong points you presented to him or her previously and how he or she can benefit from working with you.
Enter down two lines and write your closing. Keep your closing line consistent with the tone of your salutation and body. For example, if your thank-you letter is informal, you could end with "Take care" or "Talk to you soon." If your letter has a formal tone, consider ending with "Sincerely" or "With regards." Enter down four lines and type your full name. Enter down one line and type your official job title.
Print out your business thank-you letter on company letterhead, if possible. Sign your name in the space between your closing line and your typed full name near the bottom of the page.