The headline of any ad or sales letter is where you must immediately capture your readers attention to have any chance of getting them to read on about what you have to offer. You have only a few seconds to get this done.
Always (and I mean always) put your self in the "shoes" of your reader.
Think about this for a second...When you read someone else's ad, what do you want to know? Do you want to know how great their "Wiz Bang" (or what ever their offer) is? Or, do you want to know how that "Wiz Bang" is going to help you get what you want or need? You want to know what's in it for you, right? The headline must convey that what ever the offer is, it's going to benefit you to read on.
So what ever it is you have to offer, put the biggest benefit of your product or service in the headline...Tell them what's in it for them so they will read on or click on your link.
