Nearly the most important aspect of a website design is its usability. "Usability" is an umbrella term embracing the entire visitor experience while on your website. Is important information easy to find? Do links carry you logically to related content? Following several key guidelines can help keep your site visitor experience from devolving from interest into frustration.
1. If everything is important, nothing is important. Parts of your site will be more important than others and the most important parts should be visually emphasized. If minor or incidental content receives the same visual emphasis, then the visitor cannot quickly grasp the site purpose.
2. All the elements in a design have to contribute to the overall "look." No matter how cool one element might look when considered by itself, if it doesn't contribute to the overall feeling, it is a distraction and should be redesigned or eliminated.
3. The user interface should be consistent and intuitive. Navigation links should have a consistent look and feel throughout the site so that a visitor doesn't have to guess whether or not an image or text is a link.
4. Text being emphasized in the content should never be underlined; bold face or italics should be used instead. An underline is a universal symbol for a hyperlink, so visitors will think that the text being emphasized is a link. If it doesn't link somewhere, they will feel like the site is "broken."
5. Key features of the page layout should be consistent. If having a contact form on the site is important, it should be in roughly the same page location throughout the site so that a visitor never has to look for a way to contact you.
6. Minimize the number of clicks a visitor needs to make to get to important information. The rule used to be not more than three clicks to get anywhere important. Many designers would now say that the number of clicks should be not greater than two.
7. The text used for a link should be quickly replicated on the page linked to so that a visitor is reassured that the click has taken them to the correct page.
8. The technology constraints for a site (page width, advanced scripting, Flash version, CSS features, etc.) should always be based on the average user's technical capabilities, not the most advanced internet user. The exception would be if the site is only intended to appeal to high end users. 99.99999% of websites do not fit into this category.
These guidelines are just the tip of the iceberg when it comes to designing for usability and a positive user experience. But they are a great starting point.
