Write the sender's address on the upper left hand side of the letter. Don't write your name, business or title, as you will address this later.
Write the date on the line underneath your address.
Write the inside address below the date. This is the address that your business letter is going to go to, or the recipient's address. Try to address it to a specific person whenever possible.
Begin your letter with a formal salutation or greeting. Formal greetings can include "Dear" but should be personalized. If you don't know the name of the person you are writing to, try to find a title, or do some more research until you find a person's name. A formal business letter should always have a person's name.
Write your congratulatory letter in three paragraphs. The first paragraph should explain who you are and why you are writing to the recipient. The second paragraph should be the congratulatory paragraph, in which you give an announcement, or offer praise or simple congratulations. The third paragraph should wrap up the letter. If the person should contact you, or if you have any other information you'd like to give them, place it in the last paragraph.
End your letter with your closing remarks, a closing such as "sincerely" and your name and title.