The key to designing a landing page is optimizing it for conversions. While there is no set formula that works for every company every time, there are some guidelines that can help get you going. The most important thing to do is get your landing page up there and start A/B testing different elements. I've come up with a quick and dirty landing page best practices guide to help get you started.
The two areas you need to focus on when considering landing page best practices are the layout and the language.