As more and more users gain access to the web it becomes increasingly important to ensure that your website is accessible to all, not just a few. Just as businesses must comply with the American Disabilities Act to ensure proper access to customers with disabilities, businesses should do all they can to make their websites accessible to all users regardless of the means in which they access the site.

And of course not all accessibility issues involve meeting the needs of the disabled. What must be considered is the growing number of users that now access websites through non-traditional means, whether it be mobile phones or with images turned off. These users can still be your target audience and ensuring your site can be used through alternate avenues is essential to capturing that audience.

Doctype declaration

The doctype allows you to declare what version of HTML your site uses. This is helpful to the browser rendering the site so it knows how best to interpret the information presented. Each page of your site should specify doctype and language encoding. If you are unfamiliar with the doctype declaration, you can read about it at W3.org.

Page defaults

Use your Cascading style sheets (CSS) to set all the default colors, font sizes, and text alignment of the site. Different browsers use their own defaults for any of these and failure to set them to your preference may cause your site to look quite different than intended in different browsers.

Resizable fonts

Site should use relative, rather than absolute, font sizing. Relative sizing allows visitors to resize the font to their preference. You lose some control over how the page appears but better to lose a little control than to lose the visitor all together because the font is too difficult to read.

Bulleted lists

When using bulleted lists be sure to use the proper list markup, (UL, OL and DL) and (LI, DT, DD). While you can insert bullets with code or using an asterisk, using the proper markup is the best way to ensure that it renders properly across multiple platforms.

Alternate image text

All visual images on a page (not those used for page formatting) should contain alternate text describing the image. This ensures that the image is properly described for text readers and those surfing with images turned off.

CSS-less browsing

Many devices don't use CSS when rendering a web page. Make sure that your site can be viewed and browsed satisfactorily when CSS is turned off.
These are just a few quick accessibility issues that should be adhered to. While most users are still using traditional browsers, mobile phones are becoming more widely used for web surfing. Designing your site with accessibility in mind assures that it scales properly for different browsers, mobile phones, screen readers, etc. By doing this you'll capture more of your target audience.