Summarize:

The two most common formats for formal letters are block style and indented style. With block style, every part of the letter will be aligned with the left margin. Indented style requires that you indent the beginning of every paragraph, as well as the sender’s address, complimentary close, and the signature. The differences in these are largely a matter of preference; however, block style is more commonly used in business letters today. This can be either your home or business address, depending on whether the letter is sent on behalf of you personally or on behalf of your company. You should include your street address, city, state, and zip code, but you should not include your name.  If you are writing your letter in block format, your address should be lined up with the left margin. If you are using indented format, start one tab right of the center margin.  Phone numbers and email addresses are generally not included in the sender’s address, but they are acceptable. This should be the date that the letter was written. There should be a space between your address and the date, and 2 spaces between the date and the recipient’s address. Two spaces below the date, type the recipient’s name, including their courtesy title, such as Mr., Mrs., Ms., or Dr. Use the same courtesy title used in the salutation. Beneath the recipient’s name, include the full name of their company, if you are writing a business letter. For personal formal letters, you can omit the business name. Follow with the full address. As with the sender’s address, this should include the street address, city, state, and zip code. If your letter is addressed to a company or a specific department, you can include an attention line to direct the letter to a specific individual. This would come 2 spaces below the address and 2 spaces above the salutation. The salutation would be directed to the company or the department. The salutation is a greeting, and is likely the first thing your recipient will read. The salutation should be aligned with the left margin. Examples of salutations might include "Dear Mrs. Wells:" or "Dear Professor:" If you used the block format, your body, complimentary closing, and signature will all be aligned with the left margin. If you used indented format, the body will be left aligned with each paragraph indented, and the closing will be one tab left of the center, in line with the sender’s address. The complimentary close should be a phrase such as “Best regards” or “Thank you” and should be followed by a comma. Only the first word is capitalized. Skip 4 lines, which is the space for your signature, then end with your name.
Choose between block or indented format. Start with your address. Include the date one line below the sender’s address. Begin the recipient's address with their name. Follow the recipient’s name with their business name and full address. Include an attention line if you are writing to a business. Write your salutation one line beneath the recipient's address. Follow with the body and the closing of the letter.