Here is a short video that give a great introduction to web usability. Take a few minutes out and watch this short presentation from CanadaHelps.org.
It's a great starting guide in identifying factors on how to make your web site more easy to use and create a better user experience for your web visitors. It also starts you off on creating a basic usability test for your web site.
Basic Website Usability Tips from CanadaHelps on Vimeo.