Websites should be accessible to all users. Two important points to consider are accessibility and usability.
Accessibility removes as many barriers as possible; for example, optimizing a web page so that it can be navigated with a screen reader.
Usability is a qualitative measure of how easy a web site is to use and navigate. The World Wide Web Consortium (W3C) has issued accessibility guidelines, and the WAVE web accessibility evaluation tool can be used to evaluate individual web pages. Usability.gov is an excellent resource for exploring the basics of user-centered web design, and includes free downloadable templates.
Maintaining an accessible website can help libraries achieve compliance with the Americans with Disabilities Act (ADA). More information can be found on the ADA Best Practices Toolkit for State and Local Governments.