Follow google optimization tips which are there on adsense.blogspot.com Make your ads blend with your site theme colour.
I think CTRs weigh heavily on the niche of the site. Certain topics are bound to have more click throughs, while others not. Just hit the content hard, and make sure the ads are pertinent to your website. -Nick
get genuine traffic and follow the points mentioned in the abve posts. simple as that-but the former part is not easy!
i do not suggest having a site that has amazing blending to the point of people accidentally clicking your adds. Sure you will have nice payouts for a few weeks, then suddenly you will get a huge drop in Cost per click, because you will be smartpriced. Those sites with not much content and that don't exactly hit what users are looking for will see nice CTR and not get smart priced