The first step to creating resumes and cover letters is to understand what they really are and how to best use them in a successful job search. Most people think a resume is a document that traces one’s work history and skills. The cover letter is a formal accompaniment to the resume, intended to introduce a job candidate. But resumes and cover letters are also much more than that. They are marketing tools to get the attention of your desired audience—potential employers—and interest them in learning more about a quality product: you. How do consumer products companies get us to buy their products? Marketing. How do financial services companies attract more customers? Marketing How do political candidates move their campaigns forward? That’s right, marketing.
Viewed this way, it’s easy to see how important a cover letter and resume are to a job search—and how much potential these marketing tools have. But any successful marketing campaign requires a carefully crafted message that speaks directly to the needs of its audience. Your resume should make recruiters say, “Yes! This is exactly who we need. I want to meet this candidate to learn more.”
source : Killer covering Letters