Write a rough draft of your business letter. It is usually easier to write the basic content first, and then find and correct any punctuation errors afterward.
Insert the proper punctuation for the salutation and the closing. In business letters, the proper punctuation mark to use after the salutation is a colon, and the proper punctuation mark to use after the closing is a comma.
Correct any punctuation errors you may find in the body of the letter. Conventional punctuation rules apply to the content, so consult any reputable source of punctuation and grammar guidelines if you are unsure about whether you are using punctuation appropriately.
Proofread your letter. Because business letters are used for professional purposes, it is important that you take a final opportunity to review your letter to ensure you did not overlook any punctuation mistakes. If you are still concerned about your punctuation use after proofreading it yourself, have a friend or family member look over your letter as well.