Ahhhh! Cover Letter!

My tip would actually be not to write one. Unless you are very certain that they are still used in that industry. Where I work, we read the cover letters people write and laugh at all the cliches used in them (so don't use cliches if you do write one!). But then we throw that resume in the trash because anyone who writes a cover letter isn't someone the company wants. They are shooting for a higher up job if they're writing a cover letter, and those jobs just aren't available. But I would imagine that in academia and other fields cover letters are still written, in which case you should write one. Just make sure that it is original.