For the most part, my instructional resources are fairly accessible. In designing any written or web published content, I avoid using the formatting tools of bold, underline, and color to call out my text and instead use the Header hierarchy and I use ALT text for images. This allows screen readers to more accurately reflect content for those who are visually impaired. This is something that I always cover in trainings that include the Header hierarchy features. I also try to make the font larger for easier viewing.
In creating videos, I always include a script for any voice narration and upload this script as a .txt file so that it more accurately syncs for closed captioning. I also make the script available through a downloadable transcript for viewers who have hearing disabilities. I do not rely upon the built-in transcribing on YouTube as I've seen inappropriate transcripts created. Since I am already writing a script, I find it best to use that as the transcript.
In selecting colors, I try to avoid color combinations that are most common for those with color blindness. When using color, I try to balance the different hues/values so that should someone be color blind, they will at least be able to see shades of gray.
Finally, I try to create hierarchy out of the structure of the content - whether it be text or images - so that more the important information is more obvious.
Although I feel that I am making my instructional resources accessible, I am sure that there are even more edits that I could make. The Web Accessibility Initiative website has great information as well as checklists for designers. Another good resources is the Health and Human Services department's Section 508 Compliance page that not only addresses websites, but other common documents (Excel, Word, etc.) as well.