Thanks for replying. I realise now that my question was unhelpfully vague.
Sure, but you can still answer questions like 'does this game follow a set story, the DM's story, or is it driven by the player characters?'. That's just low-hanging fruit. People who want to drive the story with their characters will not enjoy being railroaded. Maybe the DMG has something on this, and I missed it. If people want to quote chapter and verse at me, please do!
Presumably, as a developer, you know (hopefully!) what it is you're supposed to be developing, and have various metrics or milestones to meet. As an inexperienced DM, how would you even know what it is you should be looking for? 'My players show up and seem like they're having fun' is a minimal baseline.
All I can say is that we figured it out back in the dark ages before personal computers and internet. I find it difficult to believe that anyone that wants to DM can't spend an hour watching videos to get an idea of how to do it. They've probably spent years playing video games. None of the concepts for DMing are rocket science.
Of course new DMs will make mistakes. I've been DMing pretty much since the inception of the game and I still make mistakes. I just don't see a significantly better solution than what we already have. As far as players not having a clue, I've had players that have played for years without seeming to have a clue.

They started doing a game intro video, DndBeyond now has a getting started page. I haven't looked at it, but I think it's a good start. There's only so much you can learn from a book and different people learn in different ways.