Do your research before starting your email. The organization’s website and LinkedIn are good places to start. General Google searches can also turn up useful information.
Learn what you can about the company’s history, what it does, and who their clients or customers are. Try and work some of this into your email to show the employer that you’ve done your homework.
Additionally, talk about the company’s needs and how your unique skill set is tailored to provide the solutions they require. Make it clear that you’ve given the position thought, and that you’re not just sending resumes to every company you can find (even if you are.)