Allowing your visitors to register is a first step to create user involvement. If you want more community interaction, you might consider enabling your visitors to rate articles. This option is built-in; when editing an article, navigate to Parameters (Advanced) and set Article Rating to Show. Now, users can rate an article on a five point scale from Poor to Best.
If you want to enable visitors to rate articles, you may want to set this for all articles at once. Navigate to the Article Manager, choose Parameters and set Article Rating/Voting to Yes. This will enable article rating for all articles you write from now on, unless you disallow rating for specific articles.
Another great way to get visitors involved is to allow them to post comments to your articles. This gives them an opportunity to give feedback on the subjects you cover and to participate in discussions with other visitors. Moreover, it can show you which issues your site visitors...