Like the brainstorming that goes into the development of a website's purpose and goals, user testing can be an important part of the development process. This is particularly true when developing on a broad scale (as opposed to defining the particularities of a site and user behavior.) Differences between intentions and actual behaviors can sometimes be found and thereby addressed.
Depending on the time and scope of the testing schedule, there are two approaches:
Selecting who to test can be problematic. Your target audience is the ideal subject. Testing can be done on a focus group or individually. Any mailing database that you have available would be an good starting place. Your assessment of who your audience is might point to a number of related organizations with likely candidates. Besides newsgroups and mailing lists, social media is a venue that may attract interested parties. Outsiders, people not planned for, can be useful. Quite often, though, some sort of compensation or gift is usually required in order to get anyone interested enough in your efforts to take the time out of their day for you.
Task analysis should be done, ideally, by someone other than those who created the site. It is generally better – especially for large-scale projects – to have a professional consultancy handle this. Getting a non-biased and scientific result requires rigorous methodology. Beyond focus groups and individual testing (utilizing screen captures and various recording devices), things like usage tracking and areas for questions and suggestions can be incorporated into the actual site.
Once you have the results of your surveys and suggestions, look for patterns of reactions. If everyone is pointing to some awkward construction, its time to go in there and fix it! And while not every response and issue can be resolved, it has been suggested that an 80/20 rule be applied towards the constant construction that is the nature of web design.
Here are some user testing resources: