Start with the headline first.
You’ll of course have a basic idea for the subject matter of your blog post, article, free report or sales letter. Then, simply take that basic idea and craft a killer headline before you write one single word of the body content.
Why?
Your headline is a promise to prospective readers. Its job is to clearly communicate the benefit that you will deliver to the reader in exchange for their valuable time.
The thing about promises is, they tend to be made before being fulfilled. Writing your content first puts you in the position of having to reverse-engineer your promise. Turn it around the other way and you have the benefit of expressly fulfilling the compelling promise you made with the headline, which ultimately helps to keep your content crisp and well-structured.
Trying to fulfill a promise that you haven’t made yet made is tough, and often leads to a marginal headline. And a poorly-crafted headline allows good deeds to go unnoticed.
Source: http://www.copyblogger.com