Unity 3d Ui Essentials, Paperback by Jackson, Simon, ISBN 1783553618, ISBN-13 9781783553617, Like New Used, Free shipping in the US

If you have a good understanding of Unity's core functionality and a decent grasp of C# scripting in Unity (although not essential if you are just using the Editor with the new UI), you'll be well placed to take advantage of the new UI feature set.