I have seen quite a lot of AdSense publishers posted in different forums stating that their AdSense accounts were banned by Google due to fraudulent clicks. Most of these people claim that they are innocent and have never clicked on their on AdSense ads. So they have no idea why click fraud can occur on their AdSense accounts. The truth is click fraud can happen in several ways and not necessarily caused by the AdSense publisher himself/herself who accidentally clicked on his/her own AdSense.
Below are some of the tips to protect your AdSense account:
1) Do not use autosurf programs to promote your websites that contain AdSense. Autosurf programs can substantially increase your website traffic or hits, AdSense page view and ecpm but people who surf your site only to earn advertising credit or other type of incentives. So the traffic generated from autosurf programs aren't counted as real and thus against AdSense policies.
2) If possible, do not involve in any traffic exchange networks and programs. If you have join one or more programs or networks that can make you a steady AdSense commission, you should start worry about your AdSense account as this could mean that members of the program(s) were clicking each other AdSense ads all the while whether intentionally or unintentionally. As soon as Google detected a group of people were clicking each other AdSense, many of the members AdSense account in the program will be suspended. Also traffic exchange can be another mean to artificially generate tons of unreal website traffic or hits and boost up AdSense page view & ecpm and it is strictly prohibited by Google .
3) Do not join AdSense exchange networks. They are similar to traffic exchange programs except members are participate just for clicking each other AdSense. This should be a guaranteed way to be banned by Google.
4) Read all the Google AdSense policies at http://www.google.com/adsense to see whether you have against any policies and make the necessary modification.