Why standards?

Web standards are developed and supported by The World Wide Web Consortium (W3C) so the Web will function well for all users.

Using standards

Separate page content and layout structure

Use CSS to control page layout and style. Minimize the use of tables and image spacers for page layout. Avoid inline styles (font tags). This technique allows screen readers, older browsers, and non-standards compliant browsers to view page content as gracefully as possible. Design changes and updates are easier to make across entire sites without disturbing page content. CSS helps create smaller file sizes, allowing faster web browsing.
Avoid building pages for just one browser

Common standards ensures the content will be viewable by the widest number of browsers. Building to one standard is more efficient. It eliminates the need for specific browser tricks/hacks, browser sniffer detection, and specialty code.
More information
1. The Web Standards Project
  A grassroots coalition fighting for standards that ensure simple, affordable access to web technologies for all.
2. Web Standards Group
  Web designers & developers who are interested in web standards (HTML, XHTML, XML, CSS, XSLT etc.) and best practices (accessible sites using valid and semantically correct code).
3. W3C's Web Standards Switch
  W3C's Web Standards Switch or how to improve your Web site easily