This is a continuation of this month's series on common cover letter mistakes and how to avoid them. Last week's mistake was making the cover letter all about what you want.
Another problem I see on cover letters is repeating what's on your resume.
Your cover letter should reference what's on your resume, but not repeat it.
Sometimes I read cover letters that make it seem as if the applicant thinks the hiring manager will read either the cover letter or the resume, but never both, so they use their cover letter to summarize — or, in the most painful cases, recount line for line — what's on their resume.
In truth, whether a hiring manager looks at the resume or cover letter first will depend on their personal preference. (I tend to look over the resume first to see if the applicant meets the minimum qualifications before reading through their cover letter.) But if the hiring manager likes what they see on one, they're more than likely going to read the other as well.
Assume the hiring manager has read or will read your resume. Use the cover letter as an opportunity to tell them what they can't get from reading your resume.
One way to know if you're running into this mistake is if you mention multiple jobs chronologically (as in, "First, I did this, then I moved to this company, and now I'm at this company").
Ask yourself, "Can this piece of information be found by reading my resume?" If the answer is yes, you can probably take it out of your cover letter.