It is important and of great help to know how to write business letters. Why? Because it is to your advantage to write an excellent letter. Also, if you plan to take the GED test, there is a strong possibility that this will be on the test. In either case it is well worth learning the techniques.
On the top left hand side of your page, write your first and last name on the very top line. On the second line type your street number and the name of the street, on the third line, type in the city you live in, place a comma after the city, then put in the state. Don’t forget to put in your zip code after the name of the state.
Now go to the left hand corner of page and skip two spaces from the address line and put in the date. Skip two spaces after the date line, and write the name of the recipient. If this person has a job title, place a comma after the name and type in the title. On the next line type in the name of the company. On the third line, type in the address, and in the last line, as you did with yours, put in the city, state and zip code.
Now you are ready to skip two spaces again. You can start with Dear, followed by Mr., or Mrs. or Miss, or if the person is a doctor, then type in Dr. before the name. If you want to be more formal, you can address this person as Dear Sir or Dear Madam.
You are now ready for the most important part of your letter, the body. Again, skip two spaces. You do not indent, but make sure you put spaces between paragraphs. It is important to put your main idea or what we might say the reason for your letter, in the first sentence of the body. Make sure you write to the point. Don’t ramble. Remember, this person, no doubt, has a great deal of letters to read.
Now we’re ready for the proper closing. The most common is Sincerely or Yours truly. Make sure Sincerely or Yours is capitalized and place a comma after whichever closing you typed in. (Yours truly,) or (Sincerely yours,) Here again, you skip a space from the body of your letter and place the closing on the left hand side of the page. Type in your name after the closing
After your letter is completed, check for spelling and grammatical errors. If you are working, and have access to company letterhead, then use this instead of you own stationery.
Source: How to Write a Business Letter