To see a model for this, look to companies with B2B DNA. Facebook and Twitter are used to taking a "PM knows best" b2c approach, not a "customers first" perspective. Salesforce REST is a good example from larger companies (disclosure - my cofounder was one of it architects), and Stripe's API is a great example from the startup world.

From studying these, I found that the best practices aren't all that surprising: versioning, discoverability, and following HTTP standards.