Everyone developing APIs struggles with API design. Ok, maybe a few of the gurus out there don't, but the rest of us need education, practice, and ideally someone or something to help guide us through the best practices when it comes to API design. I try to track what different companies are doing when it comes to API design, and maintain a list of any API design guides I come across in my work.
If you are looking to start getting a grasp on API design at your company, organization, institution or agency, I recommend starting on the journey to define your own API design guide--you will be surprised what you can learn along the way. You can kick things off by visiting my API design research, but I strongly recommend you head over to the API Stylebook, and build on this important work.
My friend Arnaud has aggregated 12 of the leading API design guides out there and is currently processing Google's API design guide, adding more knowledge to the repository. He takes each API design guide and breaks them down into common API design topics that you can consider as part of your own process, and resulting guide. His work is all machine readable and forkable so that you can easily assemble your own guide, and get to work learning, defining, and refining--then you can submit your guide to the API Stylebook when you are ready.
API design and API definitions are the top two most trafficked areas of my website in 2017, and most of 2016. API design is top of mind for API providers who are further along in their journey, and the ones who are seriously rocking it usually have some sort of guide, helping keep things consistent. If you need any help, feel free to reach out. I am not an API design expert, but I know my way around the finer details, and concepts at play, and I'm happy to help where I can. I know Arnaud is happy to answer questions as well, and if nothing else, let me help tell the story of your API design journey so that others can learn from it.