For a blog, placing 1 ad in the header and one text ad at the bottom or each post has seen the best CTR in my expreience, for non-post pages, a sidebar image ad can be of slight benefit but your main target should always be your post pages.
For a non-blog, breaking up the content of the website can achieve the best results, take a look at Gas Bill Calculator to see what I've done. Initially, I ran only a sidebar ad then when I redesigned the website I created a break between the intro and the calculator and revenues have increased hugely.
Once again, in my experience I've found running fewer, better placed ads better for CTR than running more poorly placed ads. You'll likely find one particular ad will out-perform every other ad on any given page.
Ensure your ads are blended with the style of your website. Ad link color should match the link color of your site and text should match the font (where possible) and color of your websites font and color.
Experiment, experiment, experiment. Try different styles and ad types to find out which bring the best results and ensure your abide by the AdSense policy.
