Headlines are difficult. There are a lot of formulas that can help you write good ones, or at least avoid writing bad ones.
Here's a new formula for writing headlines, from the KISSmetrics blog: Can You Write a Better Headline Than This? Not Using Old Headline Formulas You Can't. Here's the formula:
Specificity
Helpfulness
Immediacy
Newsworthiness
Entertainment value
(Read the whole post; it has a lot of helpful detail on each of these elements.)