Once your site's up and running, you can learn from it - every day...How you can track what a visitor actually does once they've found and entered your web site...
The most popular - and free visitor tracking/behaviour tool - is undoubtedly Google Analytics (GA).
At first sight the GA tool may not appear to be immensely user-friendly, but stick with it and you'll eventually begin to see behavioural trends and patterns emerging, which you'll find illuminating and valuable.
Among many other benefits, GA shows you how many visitors you're attracting, how long they stay on your site for, where they come from and which pages of your site they find the most - and the least - interesting.
The feedback you get from GA is useful in its own right, but you can also use the data to make pages of your site that visitors aren't interested in more interesting, or to further improve the attractions of pages that visitors are interested in.
For the moment that may sound a bit remote and something of a luxury, but please make sure that your web site developer includes Google Analytics functionality in your web site from day one.
You'll be glad they did.