Whenever possible address the letter to a specific individual in the company, preferably by name. If this is impossible, address the letter to the personnel director, or by title, to the head of the department in which you hope to work. Use spell check, grammar check and simple direct language. The appearance of your cover letter is important. Use plain bond paper, a color that is easy on the eyes.
Ivory is good choice.
Don't sound boastful but use power words that clearly state the facts. Proofread and check for errors. Make sure your margins are evenly set. As a good job search rule, make copies of all letters sent to employers for your record. To introduce yourself and tell why you are writing to that particular company.