Set the document margins to 1 inch, and align the text to start at the left margin. Choose a traditional font, and size it between 10 and 12 points.
Type a header to include the contact information of both you and the potential employer. If you are sending it via email, only include the employer's contact information. Add the date on the last line of the header.
Begin the letter with "Dear" followed by the name of the hiring manager and then a comma.
State the position you are applying for and how you heard about it, and briefly mention your skills.
Elaborate on your skills, and explain why you feel you are right for the position. Provide specific examples of how you have put your skills to use in similar positions.
Ask for an interview, mention that you plan to follow up, and thank the potential employer for his consideration.
Type your name, print the letter, and sign directly underneath your name.