To have a successful Google Adwords campaign, it is important to link it to your Google Analytics account, and to measure the effectiveness of your paid traffic. There are several ways to do this, one of them being Ad Versions. Ad Versions appears in the Traffic Sources section of Google Analytics, and shows the statistics related to paid traffic, broken down into the different Adverts that were clicked on.  For example, I have a campaign with 10 different adverts. Looking at the paid traffic during the past month, I can see the the 9th advert listed below (which had 74 visits) has performance statistics that are way below the other adverts. Less than 2 pages per visit and just 31 seconds per visit compare poorly to all the other adverts.

This clearly shows that the advert either needs to be deleted, replaced or the landing URL changed.