If you’re interested to update your knowledge of simply get started with Web API then there are a bunch of decent books already out there. I noticed however that Glenn Block and others at Microsoft released a book as well and, at the moment, provide for free over at http://chimera.labs.oreilly.com/books/1234000001708.
To get a grasp of what’s in there:
by Glenn Block, Pablo Cibraro, Pedro Felix, Howard Dierking, and Darrel Miller
Build HTTP services that reach a broad range of clients—including browsers and mobile devices—with ASP.NET Web API. This practical guide shows you how to build evolvable HTTP services using Microsoft's new Web API framework. It included both real world design and technical guidance from members of the ASP.NET Web API team and it's early adopters. It will cover fundamentals of Web API design and how to apply them properly using the technology. You'll learn fundamentals like how to design and select a media type, how to build out your API, and then move on to more advanced topics like how to use content negotiation, leveraging hypermedia, securing and testing your API, and much much more.
While I really don't dig webooks (I love my kindle entirely too much... even Firing, as in Kindle Firing, my dev book reading...) free is a hard deal to beat.