One of the most important aspects to your website visitors’ experience is the navigation - how they get from place to place on your site. Too many times navigation is poorly thought out and can lead turn your visitors off. Here are a few simple rules for implementing effective site navigation.

1. Keep It Simple
   Don’t overwhelm your visitor with too many navigation choices. Present them with links to just the main content areas of your site. You can then provide links to deeper pages from withing those main content areas, or within your sitemap.
    
2. Think Inside the Box
   Your visitors will feel more comfortable if your navigation is in-line with common practice. If your menus are too unique or flashy, they could be confusing to your visitor, or possibly not easy for them to recognize as your navigation.
    
3. Show Them Where They Are
   With the nature of the web, it is common for visitors to arrive at you site on a page other than your home page. Your navigation should indicate to the visitor where they are on your site. If the visitor is on your “about us” page, the navigation should have some way to indicate that, whether it be showing that menu item in a different colored box, bolding the menu option, or placing an arrow beside the menu option just to name a few.
    
4. Make It Obvious To Your Visitor
   Your menu options should make it very clear where they will take your visitor. I have seen several sites that use icons or images only for the navigation, and while they may look nice and make sense to you or your web designer, your visitor may have no idea what that icon represents. Also, your text should be meaningful; don’t try to find unique ways to say things in your menu.
    
5. Keep Them Low Tech
   Avoid using flash or javascript for your navigation if possible. While most visitors browsers support these technologies, not all do, and it’s generally not necessary to use “high tech” for something that should be so simple. Also, this has implications beyond just the visitor. Search engines don’t follow javascript or flash links, so by using these technologies you are hiding most of your content from the search engines.
    

Following these rules should help make your visitors comfortable moving around your site.

I was going to include examples, but I think it would be simpler if I just point you to the great collection of bad navigation design I found at Web Pages that Suck.