Throw out the idea that resumes are a mere listing of the work you have previously done. They are, of course, much more than that.
resume is a marketing brochure for the most valuable product on the
planet … you! It's the quick-and-dirty overview, so to speak: answering
the question, "Do I want to interview this person?" You want their
answer to be "YES!"
Your cover letter is a chance to introduce yourself to the employer. Rather than summarize your resume—which they have in their possession—take the opportunity to explain why you are the best candidate for the position. Customize the letter to each employer's individual needs and convince them that you're qualified.
Focus on accomplishments
Getting your resume to stand out from hundreds of others is a challenge. You know this already. Show what you specifically accomplished at previous internships, jobs or clubs, instead of describing your responsibilities. For example, rather than "Performed fundraising for a children's charity," say "Raised $30,000 for epilepsy research by establishing a new fundraising auction that drew over 5,000 people."
Address the cover letter to the person who is doing the hiring. Their name isn't included in the job posting, you say? Chances are you can find it by looking on LinkedIn or calling the company to ask. Also, include the title of the position and mention where you found the listing. If someone at the company referred you, mention their name.
Keep it short
HR professionals and recruiters can receive hundreds or even thousands of resumes for a single, solitary opening. Limiting your cover letter to just two or three high-impact paragraphs and your resume to a page increases the chances they will be read—or at least quickly scanned and not slam dunked into the circular file.
Proofread! Proofread! Proofread!
This might sound obvious, but proofread your resume and cover letter! They should not include ANY misspellings or grammatical errors—or so much as a single typo. And don't just look over your application materials once. Send them to your friends, your parents, your dog Fido (okay, maybe not Fido) and ask them to read through your resume and cover letter with a fresh perspective. They may catch something you didn't notice, or identify an awkward sentence—or worse, the unintentional and embarrassing pun. We know people who try to be punny should be put in the punetentury… right?!?
you're asked to include your cover letter in the body of an email, send
it in the body of the email—period. If you're asked to answer a few
questions in the cover letter, answer them. (No if's, and's or but's
allowed here!) No submission instructions? It's generally acceptable to
include your cover letter in the body of the email and include your
resume as an attachment or below your cover letter.
Keep in mind, your resume and cover letter are usually the first interaction between you and a potential employer. Make them stand out against the competition and you'll get the interview.