Any communication aimed at s 2. Use the cover to make the reader take action. Tell the audience what you expect them to do. Involve the reader. Use devices that lure prospects into reading your message.
Quizzes are one good example.
The better the device fits the interests of your target audience, the harder it will work. Don't be afraid to be human. Remember you are talking to one particular reader, not a faceless crowd. Visualize that one person and talk to him. Be warm and personal.