Don’t Make Me Think by Steve Krug
Tactical advice everyone designing digital interfaces should be aware of.
The Design of Everyday Things by Don Norman
Great for understanding the fundamentals of how humans interact with interfaces of all kinds, and what’s required to make design work for people, not the other way around.
On Writing Well by William Zinsser
I believe that clear writing equates to clear thinking, and this book is the best resource I know for how to write clearly. Writing is useful for thinking through design problems and communicating ideas without ambiguity. Beyond improving writing skills, many of the concepts taught in this book apply equally well to design: simplicity, structure, and intentionality.