Simple is best 
The immediate usability of a site plays a large part in its success. Users have certain expectations how things work on the internet and they expect your site to work pretty much exactly the same as the other sites they surf on. You may find it fun to think up a whole new system of navigating on a web site or to use all kinds of strange symbols but users don't really appreciate that. They don't have the time or the energy to read yet another 'Help' or 'How to navigate' page to get the hang of yet another new system. Don't make any special pages telling users how to surf on your site but stick to the rules and standards. That way, users don't need any explanations.

Examples 
Navigation. One of the things a lot of sites feel called upon to explain is the navigation. Needless to say this is not a good idea. Navigation is a crucial element of any web site and users should be able to use it without giving it even one second of thought. Some sites use a perfectly standardised navigation system but nevertheless feel the need to explain how it works. That's not good either. 
Search. A lot of sites think they have to explain to the user what a search feature is for and how to use it. The solution here is the same: just make sure your search feature works the way it should (which is like Google and Yahoo!, sites every user knows). A search feature that works differently will only cause confusion. No amount of explaining can remedy that. How to surf? Some sites use the 'Help' or 'FAQ' pages to teach users how to surf or how to change the settings of their PC to ensure an 'optimal user experience' on their site. In both cases, the site is out of order. It's not a site's job to teach the user how to surf, and it's not a site's prerogative to make the user change his settings and preferences to accommodate one particular site. A site should work properly with any given configuration. An added problem of these explanations is that the tips are often outdated and aren't true for the latest browser versions or operating systems, making them completely useless. 
Lame excuses. Some sites take bad behaviour one step further by using the 'Help' and 'FAQ' pages to say a number of defaults of the site aren't actually the site's fault but the user's or more accurately, the user's operating system or browser version or settings. Again, make sure your site works properly on all operating systems, in all browsers and don't blame users for your site's mistakes.

Els Aerts & Karl Gilis