AdSense Setup tab>>Competitive Ad Filter link>>click Add / Edit Sites>>Click Save Changes
There are two methods of obtaining the destination URL of an ad: the AdSense Preview Tool, and viewing the link Properties.
2) (This part is tricky) Identify MFA sites. The MFA sites use arbitage to pay for a couple cents for traffic so that they can make 10x or more for a click on their site. You can use AdsBlackList.com - An initiative by Concept Business Systems Ltd
to help you or get a feel for them yourself.