You can find many articles and guides that discuss where website owners should be putting their ads to get the best response from their viewers. The majority agrees that the ads should be in the visible places so the advertisers are interested in bidding and that we shouldn't be putting ads on subpages such as archives and so on.
I personally always place ads on the top of the page above the content, one below the content post, on the left side and below comments. It has worked quite well so far or at least the statistic says so.
What about you? Where do you tend to place your ads? What sort of response are you getting?