Keep it simple. The author offers up three basic, important SEO metrics that lead the way when measuring performance. A brief summary:
Increase in visitors
This is perhaps the most important metric to pay attention to. You shouldn’t expect to see a huge increase in visitors after only one or two months, but as you continue to build your brand online through SEO efforts there should be a gradual increase. In addition to an increase in organic traffic coming directly from the search engines, you should also start to see an increase in the number of referring sites.
Increase in non-branded keywords generating traffic
SEO works to increase visits from people that haven’t yet heard of your business and that are using non-branded search terms to look for a product or a service that you provide. As an SEO campaign is implemented and evolves there should be a steady increase in non-branded keywords that are generating traffic to the site.
Increase in time spent on the site
Visitor growth is important, but what’s even more important is growth from the right kind of visitor. This is why the keyword research process is so important. Selecting the wrong keywords to target can result in the wrong traffic coming to the site that will probably leave just as quickly as they came without converting. If the time spent on the site is improving, it means that the SEO campaign is targeting the correct keywords and bringing in the right kind of traffic.
Great data against which you should benchmark activities and review/adjust your strategy!