If you have a website that isn't performing as well as you'd like, I highly recommend you visit Chris Mole's websites. These are:
If you sign up for his weekly newsletter you will receive a free 79 page PDF handbook called 'How to get more customers from your website', which covers the fundamentals of how to sell effectively on the internet.
I have found this an excellent resource. The advice provided in his email newsletter is also well worth reading. For example, the most recent one provided a definitive list of the best free online NZ directories.