•Keep it simple. Say what you want to say and be done with it. Include well defined headings and separate your content into readable chunks. Bling and flashy extras can create frustration for screen reader users.
•Good color contrast. Foreground colors should be easy to read over the background colors. Think about using: AccessColor - it is a good color contrast analyzer.
•Captioning or transcripts. Videos should be captioned – Period. If you are not able to caption, please include a transcript. YouTube offers a captioning option.
•Labels. All images and tables that display useful content should have a description with the basic point the image or table is trying to portray. Screen readers such as JAWS rely on these descriptions.
•Text size adjustment. Most modern browsers allow for text size adjustments through the “ctrl ++” or “ctrl -” commands. Use text wraps to prevent the text from crowding when enlarged.
•Keyboard navigation. Provide keyboard access points to allow screen reader users and other non-mouse users to navigate the page. Include a skip content option so that the keyboard commands don’t have to slog through unwanted information
Source: Integrating accessibility features into technical content: http://www.scriptorium.com/2012/04/integrating-accessibility-features-into-technical-content/