Your resume is a compilation of credentials that lets potential employers know what you have achieved. Your cover letter tells them why your achievements are important and why you are a good fit for the position you are applying for. It acts as your spokesman and markets you to prospective employers.
A good cover letter should have three sections: a brief opening, middle and a closing. Each part contains crucial information and needs to be strongly worded.
The Opening Paragraph
It is here that you clearly identify the position you are applying for. Tell the reader how you learned about the job. If you are responding to an ad you saw or if a friend referred you, say so. More importantly, explain why you are interested in the job or in this company in particular. Make them believe you want to work at this company, in this position.