Dave Marshall is in the process of building a "RESTish" web service and has shared some of his planning steps in a new post to his blog.

This post is going to describe how I've ending up designing, what I consider to be a fairly RESTful web API. I'm far from being an expert, and this is definitely the closest thing to a RESTful API that I've ever created, so I'm not even experienced with REST APIs. [...] Until about 6 months ago, I'd always been sceptical of creating RESTful APIs, but I think I've had a few pennies drop since then that have made me fairly confident that I grasp the basics pretty well.

He touches on topics like: authentication, the Richardson Maturity model, HTTP verbs, sample request and response messages and some BDD-style tests to predict the output of a basic request.