Not a complete picture, but please make sure you have enough contrast. Even this very site is a bit guilty, but Apple's stuff is especially bad about having gray text on a slightly darker background, making it hard as hell to read. Please put enough contrast! https://www.contrastrebellion.com/

Also look at more modern government websites, from both the US and UK. They aren't pretty in the conventional sense, but they work!

https://www.gov.uk/guidance/government-design-principles

https://designsystem.digital.gov/

Good examples:

https://www.healthcare.gov/

https://bmv.ohio.gov/