From http://www.w3schools.com (Copyright Refsnes Data)
Your users will use different hardware and software.
The important thing is to KNOW YOUR AUDIENCE.
Remember that not everyone on the Web has the same monitor as you have. If you design your Web pages to be displayed on a monitor with a 1024x768 resolution, some of your visitors with lower resolution monitors (like 640x480) might have problems reading your pages.
Some users still have low resolution 640x480 monitors, but the trend is moving towards 800x600 as the low resolution standard. This Web site is designed to be best viewed on 800x600 or better resolution.
If you are one of those developers with a sophisticated monitor (1600x1200?), make sure you test the display of your Web pages on different monitors with lower resolutions.
One wise thing to do when designing the layout of Web pages is to let a section of each page be of variable size to fit the size of a large or small resolution monitor.
Take a look at our browser display statistics to see the trends in monitor development.
Both of the two major Internet browsers (Netscape and Microsoft) have their own specialties and quirks that you must consider when designing your Web pages.
If you are serious about your Web site, don't forget to test every page with different types of browsers.
The most popular browsers today are Microsoft Internet Explorer and Mozilla Firefox.
Additionally, some of your visitors might use text only browsers, such as Lynx, or they might visit your site from an online service like AOL, CompuServe or Prodigy. Some of these browsers might not display your Web pages as well as you think.
One wise thing to do when designing Web pages is to use strict, formal and correct HTML (or XHTML). Strict and correct coding will always help a browser to display your pages correctly.
Take a look at our browser statistics to see the trends in browser development.
Some elements in your Web pages, like sound and video clips or other multimedia content, might require the use of separate programs (helper applications or plug-ins).
Don't use such elements in your Web pages unless you are sure that your visitors have access to the software needed to view them.
Some people have serious viewing or hearing disabilities. These users might want to visit your Web site.
Some of them will try to read your pages with Braille or speech-based browsers. Remember that all of your visible content is lost if you don't provide them with some text based alternatives for pictures and other graphic elements.
Designing Web pages for people with disabilities is not an easy thing, but one small thing you can do - at least for people with poor eyesight - is to let your pages use a resizable font size.
(Have you ever tried to change the text size while browsing W3Schools?)
From http://www.w3schools.com (Copyright Refsnes Data)