Understanding the philosophy behind the REST Architectural Style is recommended for developing good HTTP-based services. If you are new to RESTful design, here are some good resources:

[REST Dissertation][fielding] -- The chapter on REST in Roy Fielding's dissertation on Network Architecture, "Architectural Styles and the Design of Network-based Software Architectures"

[RFC 7231][rfc-7231] -- Defines the specification for HTTP/1.1 semantics, and is considered the authoritative resource.

[REST in Practice][rest-in-practice] -- Book on the fundamentals of REST.

These guidelines are applicable to any REST API exposed publicly by Microsoft or any partner service. Private or internal APIs SHOULD also try to follow these guidelines because internal services tend to eventually be exposed publicly. Consistency is valuable to not only external customers but also internal service consumers, and these guidelines offer best practices useful for any service.