While the contents of your resume are important, they are fixed. You can't change your past or your qualifications.
Your cover letter, however, is a fluid document. It's an opportunity to fill in any holes in your resume or to address any concerns. Handled correctly, a cover letter can explain to the person doing the hiring why you deserve an interview.
Consider every cover letter to be an opportunity to make a case for yourself. This isn't a standard document you tack onto every job application. Instead, it's a living, flowing letter that allows you to explain why you are right for the job, even if your resume does not make it obvious.
Here are three ways to make your cover letters more effective:
1. Address the job ad
Your cover letter should answer any questions from the job listing that your resume doesn't. Maybe the ad asks for someone who speaks some Spanish, and it's not clear from your resume that you do. You can easily point out in your cover letter, for example, that you "took four years of high school Spanish and spent a summer living in Mexico."
Even when it's not something this obvious, use your cover letter to make it clear that you read the job listing. Pick a point or two and answer the questions asked by your potential employer.
2. Make your case
Your cover letter is an opportunity to explain why you are the right person for the job. In cases where you are less clearly qualified, that can be very important.
In my case, I once applied to be the editor of a local business journal. At the time, I had journalism and editing experience, but not specific business journalism experience. I argued that since I had spent time running a retail, wholesale, and manufacturing business, I was a unique candidate.
It didn't land me an interview, but that tactic did get me noticed. I started a dialogue with the person doing the hiring, and the next time that job came up (after I had added some business-writing experience to my resume), I was remembered and landed an interview.
3. Get it right
It's amazing how often cover letters are sloppy and full of typos and grammar errors. That may not immediately disqualify someone from getting an interview, but it's certainly a strike against that applicant.
Have someone on call who can proofread your cover letter: ideally, a friend with an editing background. If you don't have a person like that, use an online grammar checker and have at least two other people read your cover letter before sending it out.
Use every tool
A cover letter can hammer home your qualifications for jobs you are well-qualified for. It can also be your way to get attention when your resume has holes or you are a nontraditional candidate.
Take every chance to make your cover letter work for you. Don't think of it as something you have to do. Instead, see each cover letter as a unique opportunity to introduce yourself and enhance your candidacy.