1) Read it out loud to yourself. Have you missed words? Do you trip over anything? 2) Read it aloud to two or three people who are unfamiliar with your industry. You're looking or understanding and reaction. Ideally, you'll hear _ hey, do you do that? That's how you tell you've gone beyond examples of good cover letters and they're enthusiastic.
Now this may sound easy enough, as many people will resort to one of two methods for getting your letter together: