Accessibility Layout

Overview

HTML layout is one of the most important things to be aware of for screen readers. A screen reader will read the HTML of a website from top to bottom, using headings to differentiate sections of the content. If your website is not properly structured it will be far more difficult to navigate.
The safest way to structure your HTML is in a way that makes the most sense if you were to print it all out without any formatting.
Every interactive element should be accessible with only a mouse and only a keyboard
Don’t override the default forward and back button unless you have a really good reason to do so
Keep backgrounds simple and muted
Make sure your content is well-organized for users that are easily distracted. Use bulleted lists where possible to make things easier to understand
Information that is particularly important shouldn’t be buried in blocks of text. Call out the very important things

Probably just don’t use them
Make sure they’re easy to close if you do use them. The close icon should be fairly big and easy to click on.
Make sure they can be closed with the esc key, and also make sure that is written on the pop-up so a user knows that that’s an option

CAPTCHAs can be a huge issue for a screen reader as alt text can’t be included of the letters on the image.

Always make sure that there is an accessible alternative for screen reader users if a CAPTCHA is absolutely required for your website (or just don’t include it at all).
If it times out, make sure it doesn’t time out too quickly such that individuals that are slower at typing won’t be able to pass it

Use the ARIA timer role to indicate to a screen reader user that something is counting down. By default, these won’t announce the changes to the user, but this can be overridden by a developer. Be careful not to be too annoying, though!

Avoid them if you can. If you can’t:

Vet the advertiser to make sure the ad isn’t too distracting
Never use advertisements that play sound, or at least not unless the user explicitly asks for it
Only display static ads if possible
If an ad has a video element to it, only loop through it once
Place the add horizontally across an entire page, so that a user can scroll past it if needed to hide it
Don’t put any content too close to an ad
Align vertical ads to the right side of the page, so that a user can make the window smaller and avoid seeing it