Don't waste your time on generic cover letters. If you're going to bother, write a custom letter. Generic rewordings of your resume just waste everyone's time.
In my experience, odds are good your cover letter won't get read or even make it to the right person. So I don't spend too much time writing them. However, a well written cover letter will help you and could be the difference in getting a callback.
My recipe for a cover letter; rewrite their job description with your work experience. Take each bullet point and tie it to something you've done. It shows how your skills fit their needs in a way resumes don't. Bonus if you do some research on the company (something not mentioned in the job description) and also match that to your skills or interest. Also, keep it to less than 1 page.
In my experience, odds are good your cover letter won't get read or even make it to the right person. So I don't spend too much time writing them. However, a well written cover letter will help you and could be the difference in getting a callback.
My recipe for a cover letter; rewrite their job description with your work experience. Take each bullet point and tie it to something you've done. It shows how your skills fit their needs in a way resumes don't. Bonus if you do some research on the company (something not mentioned in the job description) and also match that to your skills or interest. Also, keep it to less than 1 page.