You need a good landing page with at least some basic seo (your ad group keywords) on your pages, and it helps if your design is not table based like so many I see (Use css as trophaeum says).
Include privacy policy, fax, contact, and a couple more pages as well.
Group your keywords. Eliminate low ctr keywords. Oh, a other basic seo like a little link building can't hurt. Google likes content, remember - a banner is not content.
Cheers