With your landing page you want your visitor to follow your clues and "Do Something."
When should you use a landing page? When you want your visitor to take an action that you have placed in front of them.
I found some great resources on creating efficient landing pages for you. In your marketing campaigns be sure to understand the true importance of a good landing page. No, not all landing pages are created equal, so you must learn to do them correctly. And remember, always test, tweak and test again.
There are many, many more resources out there that you can use so don't confuse yourself from information overload. And for goodness sake don't just copy these resources and do nothing. Unless, of course, you don't want your visitor to do anything.