Developers, What Resources Helped You Make Your App(s) Accessible?

App developers, what resources helped you make your apps accessible? I ask both as I would like to reach out to a couple devs and would like to be able to give them actionable feedback and meaningful suggestions of where they can go to learn about accessibility, and also because AppleVis maintains a page of developer resources, and I would like to ensure what we have is updated and helpful. Any and all suggestions are welcome and would be gratefully appreciated. Thanks!