1) Don't Make Your Site Ads Jungle:
As per the AdSense policy you can have maximum three Ad units on a single page. But some people make it Ad jungle; they definitely have 3 AdSense units but they have so many other ads which are either bought directly or from other Ad network. If you are doing so; it can not only hamper your reputation in visitor's eyes; but also AdSense can frown upon you. This is watched by big brother and can get your AdSense banned. :(
[caption id="attachment_836" align="aligncenter" width="640"] Ad Jungle[/caption]
2) Don't Have Same Make Up For All Ads:
Google AdSense policy clearly states that you can't have same look of other ad network just like AdSense. That means you can't have same background, font, colour and all for these ads. Google is known for the quality ads and they don't want their ads to be different than others. People who click AdSense ads they know the Google standards; so they Google does not want others to take benefit of their reliability and quality (and no one else would think the same too). A lot of people get their AdSense banned just because they fail to comply with this step.
3) This Will Surely Get You AdSense Banned:
Google AdSense does not allow its ads on content which contain adult content, hacking software, torrent sites and few other sites. See the full list of such prohibited content here.
Fine you are not adding any content with such things on your site; but are you checking your ads. Well certainly you should. And if your earning depends on ad revenue you must check before your site is listed as AdSense banned. See the screenshot below taken from a Gujarati Newspaper's e-version. This site is having more than 75k page views in a day. But when I saw this I was shocked.
[caption id="attachment_839" align="aligncenter" width="980"] Adult Themed Ad on Newspaper Site[/caption]
It is always advised to play safe when you have AdSense on your blog/site. You can have 2 accounts with so many other ad networks and you can re-apply once banned. But once you are AdSense banned; you can not get account that easily (only few people have got it back ).
This does not mean that you should have only AdSense ads on your site or blog. You can have such ads; but have a close watch on them. Make sure these ads are not conflicting with AdSense and Google term of conditions. And for that matter sometimes even AdSense ads might seem to be conflicting. This happens because some advertisers push adult nature ads on dating and friendship keywords. If this happens on your blog/site take the ad screenshot; note down info like time, page URL and send a mail to AdSense. If you are not having AdSense direct mailing facility (which is available to people who earn above 25$ every week); disable the ads on that page and find for the answer in Google AdSense Forum or Google Product Forums. Google staff is there and they can answer your questions on this matter.
So better play safe then sorry; check your ads on a regular interval and report anything you don't like to concerned Ad Network. They can block specific ads on your site/blog once you have requested them. Now a days most of the ad network have the filter facility as well which allows you to stop specific category of ad on your site. Real work starts after you have an approved AdSense; because it might take long to get your AdSense approved. But getting AdSense banned can be so easy and hasty.