Usability has it’s own importance in a website.Some dos and don’t s to achieve a good usability are as follows.

• Do:
  • Use ALT tags for all graphics, especially navigation graphics.
  • Use black text on white background whenever possible for optimal legibility.
  • Use either plain-color backgrounds or extremely subtle background patterns.
  • Make sure text is in a printable color (not white).
  • Place navigation in a consistent location on each page of your website.
  • Use a familiar location for navigation bars.
  • Keep the design from scrolling horizontally.
  • Use one axis of symmetry for centered text on a page.
  • Encourage scrolling by splitting an image at the fold.
• Don’t:
  • Allow ALT tags to get clipped (especially an issue for small, fixed width images).
  • Display static text in blue or underlined.
  • Use boldface or ALL CAPS for long pieces of text. These slow down reading.
  • Leave too much white space–reduces scannability.
  • Make the user scroll to find critical information, especially transaction buttons and navigation links.
  • Use horizontal rules to separate chunks of content.
  • Alternate too frequently between centered text and left-aligned text. Most text should be left-aligned.
  • Fix pages at larger than 800 x 600 pixels. Larger pages may force users to scroll horizontally.