What do you think is a good starting point for developers who want to get better at this?

For example, do you know of a good way for developers with no disabilities to get an impression of how a site works in various screen readers?

The accessibility mode in the firefox debugger is a good start.

Wow nice! I feel pretty stupid for just having looked over that all the time. It comes pretty close to what I hoped to get.

I do see some surprising behavior though, eg I ran it on WhatsApp Web, where it complains about image links that have no `alt`. But these links do have a `title`. Wouldn't every screen reader fall back to the `title` when there's no `alt`? What I mean is, is that an actual issue or just a "satisfy the tool" level thing to fix? I'm not sure how people build up an intuition for stuff like this, any suggestions?

If you are using a mac, try using the web for a few minutes with the built in screen reader turned on. It is actually pretty fun, and definitely helps get a feel for what a non sighted user would be dealing with. Your example with alt is a good one, but they should still have an empty alt if it is not needed/applicable. Here is an intro to voiceover https://webaim.org/articles/voiceover/