Accessible Software

Be mindful of color, contrast, and fonts
A website should be usable without a mouse, only a keyboard. This is also halfway to making it screen-reader friendly
Buttons and links with href are focusable. Change the focus by Tab on Chrome and Option + Tab on Safari, click with Enter
Consider people with disabilities, people using screen readers, color blind people, people with poor vision or hearing, …
Opt for bigger, cleaner, uncluttered elements
Add descriptions to your images
Use web standards. Use standard HTML tags, buttons, links, onclicks, ..
Convoluted things are not accessible
Make it clear where I am and where I can go from here. Sensible urls, clear navigation links, and breadcrumbs