How to impress employers with a cover letter?

Make sure the focus of your cover letter is what you can do for the company, as the company is more interested in how you can benefit them. They really are not interested in how they can benefit you, even though a good job will ultimately be of benefit to you and this is a given.

People who are inexperienced cover letter writers typically make this mistake and tend to make this mistake the most often, though that does exempt anyone from doing it. Employers want to know what you can do to help them make a profit and what you can contribute to the company overall. Tell them how you can contribute to the company, and the hiring of you will be a benefit to them.