Key performance indicators to watch out for:

Average Time on Site
This metric is directly related to the success of a site, and if you notice that the average visitor spends less than 3 minutes on your website, alarm bells should be ringing. The longer a person spends viewing pages, the more likely they are to find something of value and make an enquiry or purchase. In short, the longer the visit the better.

Pages per Visit
If a person views less than 4 pages on your website on average, you can be pretty sure that people aren't finding the right things for the searches they conducted. You should always strive to serve the visitor quality content and relevant content. Also, it is imperative that the navigation on your site be easy to use and follow, so as not to confuse the browser.

New Visitors
You always want to ensure that you have returning visits to the site, but equally if not more importantly is to insure a growing number of new visitors to the site. These new visitors will bring with them a new revenue stream and allow you to grow your customer base, and the amount of people aware of your brand.

Bounce Rate
One of the most important stats to keep down is the number of visitors that find your site and leave immediately. This is not only loss of potential business, but also could be costing you thousands in paid advertising that brings you nothing.

Enquires/Sales
Lastly, and more of an obvious one really, is enquiry or sales that the site generates. If you are making almost no money from the site, it is not working to its full potential. Extremely important is to measure the ROI on your internet marketing costs in relation to the amount of business the site brings the company. If it is not positive, it is probable that one or more of the above points are not optimal.