A book that I have read - and intend to reread is "Universal Principles of Design," by William Lidwell, Kritina Holden and Jill Butler. This text treats the broad topic of Human centered design in a broad and thoughtful manner.
Being a good mechanical engineer demands a strong foundation in the classic engineering arts but there is a discipline that is often under served - Human Factors. This is not just in the sense of the measurements of the average hand or foot but in the design adaptations that make us uniquely human. It is also what can move our designs from pedestrian to truly exceptional.