Having been on the receiving end of cover letters and resumes for many years I have a few words of advice to job seekers: Your first goal is to get an interview, not the job.
So, be sure to read the job description, then read the job description.
Tailor Your Response.
Your cover letter should briefly and succinctly explain how you meet the needs of the position. Give examples with supporting data if available and, equally important, let your personality show through. Do not use boiler plate content.
Rewrite Your Resume for the Job You Want.
If you really want the position find ways to tailor your resume so that it highlights how your experience, talent and successes meet the needs of the position. If you are applying for a creative position, be creative. Your cover letter and resume are examples of your creative talent, or lack of talent. Resumes created in Word will be rejected out of hand.
No typos - No typos - No typos.
Make sure someone else proof reads all of your materials before you send them in.
Did I happen to mention Read the Job Description?
The more time, effort and thought you put into your response the more likely you will be successful in landing the interview.