Ask HN: I'm writing a design book for programmers, what would you like to see?

Hey all, I am a former designer, who has moved on to front-end development. I spend a lot of time working with developers who want to know more about design and how designers think. So I am working on an eBook that is focused on design basics for programmers. I am just curious what types of topics would you all be interested in having covered? I obviously would talk about the basic concepts of design, but I am thinking about a more useful focus on UI and UX and how designers think about users. Thoughts? Thanks!