Really curious how self-publishers market their material. Do you actively advertise?

It may be worth noting that, while there's some built in marketing/advertising by going through a publisher, you probably shouldn't overestimate how much. You're still going to be doing most of the marketing, whether self-published or through a publisher.

With me, plugging the book at conferences. Trying to get people I know who read it to put reviews on Amazon. (In my experience, lots more people say they will than actually do it.) I was able to arrange a book signing at one event. Email list/newsletter if you have one. Social media. Website/blog. Etc.

Bootstrapping via conference/meetup talks seems like a good idea, thanks.

Build an email list and sell into that list. Build the list by writing relevant helpful things and post them for free with a signup link.