Sticking with the AdSense theme, I'd like to talk about another way to change up your ads and avoid the dreaded 'ad blindness' syndrome with your readers.
Simply changing the colors on your ads will greatly improve their visibility, just don't do it too much. It's not quite as bad as moving them around but it can give your readers a startle (which also causes them to read your ads that first time they see the new colors) but you'll want to be careful of how many times you do this.
Myself I change my ads maybe once a month if that to a very strong color that compliments the blog. This is why it's a good idea to have color themes of 3-4 colors running through your blog. It allows you the options of changing ad colors at any time and still having them make sense for new users.