For another famous conlang, there's a cool video where Mark Okrand discusses the process of inventing Klingon: https://www.youtube.com/watch?v=e5Did-eVQDc

(He also briefly talks about the Vulcan language at the beginning.) What's interesting here is that he was brought in for the third Star Trek movie. But there was already a small amount of spoken Klingon in the first movie, created by James Doohan. So Okrand, while he was tasked with actually inventing the language, felt constrained by continuity. He discusses trying to rationalize the preexisting bits and then extend the language coherently.

(And his enthusiasm is really clear. It's fun to listen to someone smart talk about something they're really excited by.)