As above. Google use contents of your landing page to determine relevance right? So basically your page needs to be well optimized and targeted to the keyword that you are wanting to appear for in your PPC campaign. I read that to be essentially the same as optimizing your on-page for organic SEO.
Google are trying to do the same with adwords and organic - they want to be providing users with the most accurate results, they want high CTR and low bounce rate. So for adwords, they want pages to be relevant to the users search query in the same way they do for the organic results.