Failing to comply with Google’s terms could have your AdSense account suspended. And this is why this rule is by all means the most important one of all. It’s because this is the difference between life or death.
The second thing users get wrong a lot of time is having a bad color palette for ads. Many times this happens because the publishers aren’t knowledgeable enough to change default color palettes.
Others just can’t seem to spend enough time in changing those defaults. Having bad ads that stand out is sure to push people away from clicking; whilst having something which is clearly visible yet distinctive will.
Third, of course, the position of the ads is probably the key element you should get right if you want to maximize your profits with AdSense. This is noted in a lot of places on the web and Google talks about this as well. Google can provide you with statistics which illustrate what positions work particularly well on your website.