Nokia's API Building Guide

Source

I didn't get to finish this, but there are some clever things going on like naming suggestions and some other foot-guns I hadn't thought of before. This made me smile:

Even the table of contents has great one liners that still ring true today:

Choose self-explanatory names and signatures

Choose unambiguous names for related things

Beware of false consistency

Avoid abbreviations

The best API is no API