In 2007, with the publication of Day Job Killer, Adwords became a game of 'kill the competition'. Almost immediately, software systems and membership sites sprang up to help the advertiser track and conquer his competitors' ads. Unfortunately a lot of these memberships were very expensive.

So there were a lot of advertisers who could not afford those systems or maybe simply did not want to spend all of their time tracking, spying and tweaking in order to cover the cost of their membership. They began to look around for a new direction, and early in 2008 we saw the first hints that marketers were rediscovering something that they had previously considered dead - the content network.

If you have come to Adwords in the last couple of years, you may not know that the search and content networks were once united. Google separated them to give advertisers more control in the days when click fraud was common. Most advertisers immediately (and rightly) turned off the content network for their ads.

But times have changed. Click fraud is not the problem that it used to be. Google now closes the accounts of anybody suspected of 'invalid clicks'. This is a problem for site owners because it means that any malicious kid can put them out of business by clicking their ads over and over. But for the Adwords advertiser it means that the content network is usable again.

The content network has several advantages over the search network. First, the cost per click is generally lower. Second, you do not have to fight off the competition in the same way. Third, you have a lot more control - you can specify the exact sites where you want your ad to show.

The last of these points is vitally important. When you are advertising on the content network, always specify target sites for all of your ads. In fact you should go even further and specify the exact pages of the site where you want your ad to appear.

Just like with the search network, you need to avoid having people click when they are not really interested, and you do that by picking out pages that are very closely related to your product. For example if you are promoting a dog training ebook, you will want your ad on a site about dogs but only on the dog training pages.

It is also better to limit your advertising to sites that display their Adsense above the fold - that is, the ads are visible on the screen without scrolling down. Toward the top left of the screen is the hottest area, that's where you really want your ad to be.