Ryan Florence presenting "Bringing the Web Back to the Blind".
Probably the biggest accessiblity resource on the web: webaim.org.
Use your headers for organization of content rather than for visual display. It helps blind users navigation through the content based on its importance.
Adding 'role="main"' provides a 'landmark' in the page that a screen reader can find. A blind user can use these landmarks to quickly navigate to specific sections of the page.
Html 5 includes a 'main' tag as well as others like 'article' that screen readers can use as landmarks.