Effective navigation should let a user know:
- what site they are on;
- where they are in that site;
- and where they have been.
Navigation and Search Engines
Good navigation helps search engines better understand the site structure as well as helping site users. Typically your most important documents will have the greatest number of inbound links.
Often, people will use tabs or images for their links which have a minimal amount of descriptive text in them. You can offset this by using descriptive text links in the page footer. You can see an example of this technique at http://www.search-marketing.info. It is common to have one set of navigation that is used by site visitors and another that is used by search engine spiders.