Dear (insert contact name)
Paragraph 1: Introductory paragraph which should include information about what the letter will include. You can also give some information about yourself if you are writing to this person for the first time.
Paragraph 2: Main body of letter. This section can be broken up into two sections if the content will go this far, or if you feel that there are two separate subjects to address. Stick to the business of the letter, and keep the feel formal.
Paragraph 3/4: This is a concluding paragraph where you should cover the ground that you have already mentioned. Reiterate your main message, and thank the reader for their time.