When i build a landing page the first thing I do is a Google search using the keywords i intend on using in my campaign. Then I check out the advertisers. if the keyword is real compettitive the top 3 -4 advertisers are probably spending some money for that position. They have most likely created a very affective landing page. Check out their designs and try to simulate them as closely as possible. Since their page is most likely highly optimized they would make a good template for your page. Just make sure you use your own content.