One of my favorite headline tactics is to connote something shocking, weird, confusing, odd, outrageous, or interesting. And then to explain it further in the copy.
You start with something that might seem unbelievable but doesn't tell the full story, which forces the reader into the copy to know more.
Let's say you sell a weightloss program. Your copy hinges on the idea that strict diets are bad. They slow down a dieter's metabolism and can even cause health problems.
The headline could say something like, “Fact! Most ‘healthy' diets are cold-blooded killers.” (The point is that strict diets “kill” your metabolism so to speak, but it's enough to pique the target reader's curiosity and pull then into your copy.)