Maybe you're an engineer, maybe you work with a designer. Or maybe you think that design is about using Photoshop. Maybe you just care about design. If any of these are true, then there's a lot you can learn by reading and understanding these books. They will help you understand how to solve problems for people out there in the real world.
These books cover the basics -- the foundations of designing for people. No fancy Photoshop tricks. Nothing much about visual design. Instead these books are about understanding what people need when they interact with the things you make.
The Design of Everyday Things, by Donald A. Norman The best book about designing for people. If you've ever been frustrated by a confusing parking meter, or a door than opens the wrong way then this book explains why. This book explains how the design of the things we use everyday can be improved.
Universal Principles of Design, by William Lidwell Simple, clear, comprehensive. This is a solid foundation for problem solving across all areas of design. From hierarchy and Hick's law to mental models and mapping, this text covers many of the major design principles. The book itself is laid out with one principle per page, with an accompanying page of examples. A great practical reference.
The Elements of Typographic Style, by Robert Bringhurst A wonderful, lyrical book about the art and science of typography. If you had to choose a single book on typography, this is it. This is from a man who loves letters and language. Incredible treatments on type. Sections on rhythm & proportion, structural forms. harmony, shaping the page, combing and choosing type. Phi for layouts, type as a music scale. History of typography. Type foundries and type designers. Specimens. And more. A beautiful book. You'll learn more every time you go back.
Grid Systems, by Josef Muller-Brockmann This book is here because it is about using form and structure as a system to help you solve problems. It's more a practical framework for solving problems than just a book about grids. That said, this is also the definitive early work on grid design. Muller-Brockmann was one of the key pioneers of grid design and the swiss/international movement. It includes considerations of grid and structure: baseline grids, measuring systems, units, margins, faces, construction of the type area and grid and numerous examples of type and graphics in various grid combinations. This is the kind of book that you can return to again and again, and always find something new.
As Little Design As Possible, by Sophie Lovell Breaking away from the other books a little, this is a monograph about Rams and about principles of good design. As little design as possible… There are early sketches and prototypes. There are incredible behind-the-scenes photos. There are stories about Rams and his team. There's a foreword by Ive, and the 10 principles true for all good design are laid out in one place. Incredibly inspirational book. You should also check out Less is More which is equally great.