An outstanding book by Adam Wathan and Steve Schoger which clearly explains how to go from a ordinary UI to outstanding, modern and accessible one. It would teach you what to see in a UI and what matters while keeping things simple and easy for end-users.
This book can be used as a reference while designing a page or component of your web or mobile application and quickly checking and evaluating your design choices as each section is short and clearly explained.
Would highly recommend to anyone looking for quick growth in their design game.