As helper libraries make it easier to interface with your API, potentially fostering new users, their development should not go overlooked. Use the acronym "SPOIL" to create a library your users will appreciate.
Succinct: Keep your library concise with a small amount of code. Start small and leave room for growth.
Purposeful: The library should not be an afterthought, but should be considered just as important as the API itself. Design the library with consistent mapping techniques that match frequent use cases.
Open source: Libraries should encourage community participation, and be licensed as open source under MIT or BSD.
Idiomatic: Don't write PHP-like code in a C# environment. To avoid sloppiness, only domain experts that have a full understanding of the specific language should construct the library.
Logical: If you are completely mapping the API, have a predictable method for every call. Use consistent terminologies, and don’t confuse or distract users with incongruencies.