If you are a Google Adsense publisher, you are required to adhere to the Adsense policies. If you fail to comply with the policies, Google has the right to disable ad serving to your blog/website and/or disable your AdSense account at any time.
If your account is disabled, you will not be eligible for further participation in the AdSense program. So, to avoid ban, you need to be aware of the type of content that might put you in trouble, hence the need to avoid them.
You may not place Adsense code on pages with content that violates any of Adsense guidelines. Some examples include content that is adult, violent or advocating racial intolerance. Apart from these, there are other content Adsense doesn't allow.
Because Google may change the policies at any time, please always check the link above often for updates. In accordance with Google online Terms and Conditions, it's your responsibility to keep up to date with, and adhere to, the policies posted on the page.
You can also check out "How I avoid Adsense Invalid clicks/Impressions".