Much of the guidance that makes writing on the web more accessible to people with disabilities makes content more accessible to everyone. It is helpful to:
These tips will help everyone, including those who have difficulty reading and/or concentrating, as well as non-native English speakers. For a quick start, look at these tips on writing usable content for the web: tips to quickly improve content clarity, accessibility and usability.
An excellent resource on this subject is Dey Alexander's Introduction which contains links to the rest of the series. The article Accessibility Evaluation for Web Writers provides an overview to enable you to check a web page (or site) with a particular focus on assuring content accessibility.
One area that may especially call for the skills of content creators is the description of images. These descriptions are commonly referred to as "alternative" (or alt) text, see Image Descriptions.
Sometimes, images need descriptions to assist people who cannot see them. The image may be central to conveying/supporting the message in the text on the page. At other times, however, images are purely decorative so may not need a description, i.e. an alt attribute (the technical term for "alt text").
Often, content creators are in the best position to guide decisions about image descriptions since they have worked with designers and marketing staff to select images. As a result, they understand why an image has been chosen.
Consider bookmarking Text alternatives for images a decision tree from 4 Syllables. After you have used this decision treee a few times, you probably won't need to look at it often. Consistency in how your team describes images will make the job easier, and you'll also set your site visitors' expectations.
Providing text-based information to help those who cannot see an infographic is a bit more complex and may require collaboration among content creators, designers, and developers. Keep in mind that while infographics are trendy, they do exist for a purpose -- to convey key information which can also be summarized in text. Descriptions of infographics that highlight the key "takeaways" not only help those who cannot see them, but they are also valuable to people who may be using small devices, who have limited bandwidth, or who may simply not be visual learners.
Using plain language when writing for the web can be particularly valuable to people with a range of disabilities. Using plain language does not mean "dumbing down" the content. In fact, it requires skill and a thorough understanding of content and audiences to avoid jargon, make sure your readers can find what they are looking for, and assure your meaning is clear to your audience. Here are some resources about plain language that will help you get started: