Website Usability Guidelines

Follow these usability recommendations:

Design for common browsers. Designers should attempt to accommodate 95% of browsers used by all users. You should test for most popular browsers.
Don't assume that the user has selected all browser features. Try to find out what your average user's browser setting are. Users that are visually impaired use larger fonts, users may turn off backgrounds or JavaScript, graphics, and many more features.
Design for operating system. The most popular operating systems are Windows XP/Vista (80%), Windows 2000 (8%), Windows 98 (5%), Macintosh (3%).
Design for connection speed. At work most users are using high speed access. At home two-thirds of users have high speed access.
Design for screen resolution. Most users use a screen resolution of 1024 x 768 pixels. The second most popular screen resolution is 800 x 600 pixels.