There are the basics like having good SDK/libraries references. For example, [Stripe's famous 3 panels view](https://stripe.com/docs/api) is one of many ways of displaying that information.
It does get quickly blurry when you introduce topics like:
- Explaining the main concepts of the products/API
- Quick Start Guides (multiple languages?)
- How-tos for the main use cases
- Tutorials such as how to do <use_case_x> with <specific_language_or_framework>. Do you even include that in the docs?
Then there are the features of docs:
- Button to try this function/API call
- Includes the user' API keys in the sample code if they are logged in
- all of the content in one very long page or split it up.
- etc
So HN, what do you like to see in an API documentation? from little features, cosmetics, layout or how to structure the content. I want to hear about it!