Piers Lawson wrote excellent series of articles to guide you to write RESTful web service using ASP.Net MVC framework.
There are several parts (24 at the time of writing this post). But I think the first 12 parts are good for beginners to start with.
In order to create a Web API for one of our products, I am learning about RESTful Web Services.
If you are just starting on REST, then here is the link that explains REST very clearly: How to Create a REST Protocol
To supplement this it is important to know the Common REST mistakes that developers make.