How-to - the Quick and Dirty Version
OK, after that big sales pitch about why user testing is good, here's the short version of how you can do it yourself: Sit people down in front of a Web site and make them use it. Ask them questions. Make them do sample tasks.
Ask them if they like it. Think about what they say. What do they like? What do they dislike? What do they grok? What mistakes do they make? Why?
On top of this, we've found it really useful to videotape the sessions and make the entire production team - everyone who's responsible for the features and design - watch the videotapes and discuss what they see. There's no feeling like watching someone flounder with something that everyone thought was trivial. When you see five people floundering in a row, it's profoundly humbling and profoundly helpful.
In a nutshell, it's that simple. However, some aspects deserve extra attention.