Great question, using a good foundation is one the quickest ways if you're like me and aren't an expert at accessibility. If you're in React land, reach-ui is my goto, I've heard great things about reakit as well.
Once you start getting into it, I think you'd really enjoying learning the tiny details which make elements accessible. The official WAI-ARIA guidelines and Inclusive components are my recommendations.
And finally, testing man! Loooots of testing :)