From Michelle Williamson, Drupal Developer @Mediacurrent:
Web accessibility is about making websites accessible to people with disabilities. Those disabilities include everything from blindness and varying degrees of vision impairment to a broken bone in a dominant hand to cognitive disabilities such as dyslexia.
Making websites usable by those with disabilities is not as difficult as you may have been led to believe. There are things that are considered just plain good practice in building a website that can make a site vastly more accessible to all. Here are 5 things that can easily be accomplished with most sites:
1. ADD A SKIP TO CONTENT LINK
Try navigating your website with just a keyboard. Load a page and just start pressing the tab key. Follow the outline of the content in focus as you tab through the page. Now imagine that you’re on a page with a list of 50 nested menu items down the left side of page and in order to fill out a form in the main content of the page, you have to tab through every single menu item. That gets old quickly. There’s a simple solution. Add a “skip to content” link as the first piece of content in the body section on the page that links to the page’s main content. This way, when a page is loaded, all a user needs to do is press enter and voila, they’re at the page’s main content.