There are so many reasons for Google to ban an adsense account. Any account which violates Adsense program policies is likely to get banned. So, it is always better to read there terms and take care that you don't violate any of them knowingly or unknowingly.

Some of the most common reasons why people get there Adsense Account disabled are:

1. Clicking on Adsense Ads on there own site : Some publishers click on there adsense ads out of curiosity or to get more information. Some publishers who are new to adsense may also click to increase there revenues or to see how it is actually tracked by Google.
2. Encouraging others to Click of there Ads : This is equivalent to clicking ads on your own sites. Some time back there were online groups and communities which used to click on ads of other community members and each group member used to generate good income from this. Now, such groups cannot survive anymore as such activities are no more tolerated by Google.
   
   Even using such encouraging words to support you by clicking on a web page with ads is a violation of adsense terms.
3. Showing Ads on a page displayed on Traffic Exchange : Traffic exchanges are programs where each members is shown web pages of other member for few seconds and if they wish they can click on that page or visit that website.
4. Using Black Hat Techniques of Web Promotions : Black hat techniques are techniques used to take a shortcut route to get online success. They use a number of tricks to increase traffic and convert them. Some people use black hat techniques to increase there click through rate i.e. they create a condition where the visitor has no other option except clicking on some adsense ads or a visitor accidentally clicks an adsense ads. These tricks are possible with the use of some scripts (i.e. programs) and web designing.
5. Placing Ads on Page with Insufficient Text : Google prohibits anyone from placing there code on a webpage which lacks sufficient contents. Although this is not a serious violation and they serve public service ads on such pages.
6. Using Ads on Popups : Popups are little windows that open automatically when a visitor enters or leaves a site. Some publishers try to put adsense ads on these popups to earn some money from a visitor who is leaving.
7. Trying to play tricks with Adsense Code : Making any changes in code provided by Google Adsense for placing in a web page.
8. Trying to fool a visitor : Providing a title and related meta tags on an unrelated page which has nothing to do with its title or tags is also a violation of terms. A webmaster uses this trick to attract more traffic/visitors on one hand and get better paying ads on another.
9. Doing anything that is not good for Adwords Advertisers : Over and above doing anything which is not good for an adwords advertiser is against Google's policies. An advertiser is paying to attract quality traffic to there site, they are paying to get targeted traffic which is only possible if the vistor reads there ad on a relevant site. So, doing anything which is not good for an Adwords advertiser is also not good for an adsense publisher.

Reading and understanding all these points can be helpful in avoiding violation of Google Terms and getting Google Adsense Account Disabled.

Innocent Publishers Can Get Adsense Account Reinstated

If a publisher has got his Google Adsense Account disabled and he/she can see no reasons as why his/her adsense account has been disabled. Then anyone who is innocent and can prove his/her innocence by providing relevant data such as server logs (these logs can be seen when we login to control panel of our hosted site where we upload pages) or anything he/she thinks can help.

Use Google's Online Appeal Form

There is an online appeal form provided by Google where one can appeal against there decision. People at Google do listen to such cases and most of the accounts which are found to adhere to there policies are reinstated after some time.

So, if there is nothing wrong on your part then you must use this online appeal form link to which is already given above in Resources to Avoid Disablement of Google Adsense Account along with other useful links.