What are some preparations you think people should know about in advance of migrating to Linux?

For example, I saw a post the other day detailing how to set up a Brother laser printer on Kinoite. That's not something I would have initially considered a potential problem to be solved. Another I ran into some years ago had to do with an Edimax WiFi dongle that used some weirdly specific Realtek 8812 radio, for which you had...