Here's an excellent infographic with some do's or don'ts. Most sites don't even consider them and so by observing just a few, you'll be miles ahead of everyone else and won't break the bank.
You can read the full article here: https://accessibility.blog.gov.uk/2016/09/02/dos-and-donts-on-designing-for-accessibility/
Another great resource for accessibility design is: https://www.funkify.org
They have simulators for Dyslexia, Cognition, Motor Skills and Vision so you can see what your site looks like to people with each defect.
For example, here's what CNN.com looks like to someone with Dyslexia. Notice how the characters appear jumbled.
And here is what the same site looks like to a normal person: