The way a letter begins dictates its tone. Formal letters differ from personal ones in that they are used primarily in a professional context. The intention of a formal letter can vary, but what is always desirable, is that you as the writer, appear to take both yourself and the recipient of the letter seriously. There are a set of conventions concerning both language and format that put this information across.
Think about what you want to say. Expressing yourself clearly and in a concise manner shows the person receiving the letter that you are certain about what you are saying. It also demonstrates that you are considerate of the time constraints he will likely be under. Write a draft of the letter, highlight what you believe to be the most crucial information and look to express it in the simplest and most direct way possible.
Turn on your computer and open your word processing program. Write in Times New Roman size 12 font and use single line spacing. Justify the text to the right so that in the top right-hand corner of the page you can type your contact information: name on one line and address over three lines. Then add any additional contact information, such as a telephone number or an email address, making sure to give each separate contact its own line in the text. Leave a gap of one line and then write the date.
Leave a space of two to three lines, and justify the text to the left. Begin the letter with "Dear" and then the person's title: Ms., Mrs., Mr. or Dr. and then their sir name followed by a comma. If you do not know who will receive the letter, "Dear Sir or Madam," can be used or "To whom it may concern,." Press enter on your keyboard twice, leaving a line of space before the body of the letter, this makes the letter appear more readable.
Get straight to the point. If you have met the person who you are addressing the letter to, it is common practice to inform her of where it was; "Dear Ms. X, we met at the paintbrush convention in Tuscaloosa." Otherwise it is best to get straight to the information you want to relay or have answered. Here is where you refer to your initial draft: order the content of your letter around the importance of the information you have, i.e. place the most pressing concern first and put the remaining concerns in order of priority. The conventions of formality described above allow the reader to know the type of letter she is receiving, so there is no need for a long preamble.
Imagine yourself receiving the letter you are writing. What things would let you know that the letter is formal?
Using a letterhead gives a letter more gravitas and can save time on fiddly editing.
Having followed the conventions for beginning a formal letter, don't let your language become informal, as this will be confusing for the reader.