It's very simple to have a good ad placement:
Imagine your site is not yours.
Imagine you're an advertizer and can chose the exact location of your ads on this site.
There you go. I'm sure if you take the point of view of an advertizer, you will know the best ad placement.
Don't think of adsense ads as a burden on your site, as something which annoys visitors. If it can help you, consider adsense ads as additional content for your visitors, as something of value to your readers.
Put the maximum number of ad blocks allowed, 3 adsense ads, 3 adlink (thematic links) and 2 adsense search boxes. Don't listen to those who tell you that putting less ads on a page makes the CPC higher. It's true, but CPC is not a high priority, eCPM and number of ad impression are much higher priorities. Having the maximum allowed number of adsense on a page increase CTR, which is easier to manipulate in order to achieve higher eCPM (CTR x CPC).
So for a perfect ad placement and optimized CTR, use your common sense, don't hide the ads!