Landing pages are those pages where the users are directed to when they search for something on search engines. Thus, your landing page must be impactful and should accomplish conversion goals. You should first understand what your goal is and how you can accomplish it, which will help you create and optimize your landing pages.
Google has provided few suggestions in a new webmaster help video regarding how to recover from Google penalty due to spammy links.
Matt Cutts answered to the question
“How did Interflora turn their ban in 11 days? Can you explain what kind of penalty they had, how they fixed it, as some of us have spent months trying to clean things up after an unclear GWT notification?”