Ensure you are using the same font as your resume.
Include white space in between paragraphs.
Your cover letter should not exceed one page.
Language
Use clear and concise language that is uniquely targeted to the job posting.
Be sure your letter has no grammar,spelling, punctuation or capitalization errors.
Use appropriate business language that is direct, simple and powerful. Sentences should contain facts, strong verbs and actions. Relate your points to the job.