Sheryl Burgstahler, Ph.D. of the University of Washington has created twenty basic guidelines she follows as she develops her own online courses. Although these tips do not cover every potential accessibility issue, they provide a good start.
WEBSITE ACCESSIBILITY TESTING & REMEDIATION SERVICES: Mary Gillen is an experienced Website Accessibility Compliance Auditor and Remediator. She can test your website to determine if it meets accessibility standards:
WCAG 2.1: 312 checkpoints covering A, AA and AAA W3 accessibility guidelines
Section 508: 15 US federal guidelines covered by 59 accessibility checkpoints