They know exactly how things work and where to find things. You, on the other hand, don't. Instead, get a fresh perspective. The best way to do this is to talk with your site's users. This article will help you get started.
Testing can be useful during initial development, before a redesign, or as a periodic checkup.
But there is one time when you shouldn't test. Test if you are serious about listening to users. Don't test if you're simply looking for validation. Planning the Setup All you need to get started in user testing is a user, a computer, and a pencil and paper for notetaking. These are not only unnecessary, they can actually get in the way.