All webmasters should add Google Analytics to their site. It gives a lot of information about your traffic that will help you to improve your site. Google analytics will tell you how long the average visitor is there, what percentage will look deeper into your site, the top referring keywords in the search engines, unique visits and pageviews, and statistics for landing pages, and more.

No other stat monitoring service can tell you as much about your web traffic as Google Analytics. All you have to do is first sign up for analytics. Then for each website insert a block of javascript code right before the closing body tag of each page. For example in wordpress blogs, just insert it right before the closing body tag in the footer.php file and it will cover all blog pages. With forums you can usually put it before the closing body tag in the index.php file.