In the article Deafness and the User Experience by Lisa Herrod, issues with Deaf web users are explored. And there are some excellent points for writing for web accessibility:

• Use headings and subheadings.
• Write in a journalistic style: make your point and then explain it.
• Make one point per paragraph.
• Use short line lengths: seven to ten words per line.
• Use plain language whenever possible.
• Use bulleted lists.
• Write with an active voice.
• Avoid unnecessary jargon and slang, which can increase the user’s cognitive load.
• Include a glossary for specialized vocabulary, e.g., medical or legal terminology, and provide definitions in simpler language.