The placement, colors, ad formats, etc will vary from site to site. For this reason its important to keep an Adsense Journal and continually test different variations on your own pages to determine the best combination.
That said, there are some things that run common on most sites. As far as 'best placement' for Adsense, this heat map is a huge help:
Link Units are often disregarded, but recent discussions have proven them to be surprisingly profitable. You would expect a lower CTR (click through rate) because of the fact that your visitors have to click twice in order for you to earn commission... but I've actually found (and others have reported the same) that the Link Units outperform other formats in most cases.
There are so many little things that you can do to "optimize your Adsense". Putting the ads in the content area, for example. Blending the ads with your page's color scheme. Putting the ads in headers and sidebars so that they appear to be site navigation, etc.
Anyone else care to throw in a few tips?