The short answer? As little as possible. There should be some information about your offer – but nothing too overwhelming.
And a major key to success is a minimal amount of information on the page’s form. The more fields people have to fill out, the more likely they are to not fill out a lead generation form.
Find a balance between how much information you want to collect and how much you need to collect. Unbounce.com is my go-to source when a client asks about a landing page. (And no, this is not an affiliate link. I just think they know what they’re doing). Head over to their site to see some great examples. And when in doubt, you can always run an experiment with two different forms on two pages and see which page performs the best.