100 Things Every Designer Needs to Know About People - Susan Weinschenk. This is the book from which I learned the most this year. It provides the reader with 100 applicable and up to date insights into human psychology: how people see, read, think, decide, etc. Very useful and well organized.
While UI/UX is more of a field where you get better by practice and observation, yet these books can surely help you build a solid foundation.