I like to use a real bold centered headline. This gets back to step one. You must know what is that burning issue nagging at your prospect. That's where I'd start. Look at headlines that work and adapt.
Copywriters are copy cats, and they have swipe files filled with headlines they turn to and adapt.
They may spend as much time on a headline as the rest of the letter. They select it too early. The next step is the offer. You can put your offer in your headline. Try to come up with an irresistible offer.