I feel if you want to do this, you need to define those things in the posting rules, and perhaps make a posting template, so that a new DM can make that determination when trying to make a post. As others have mentioned, a lot of new DMs aren't going to have the context to understand what information is needed to make a good post. Hell, a lot of experienced DMs probably couldn't put their style into words.

I understand the frustration, but I feel that the sub will end up throwing out a lot of new DMs as well as the bad questions if they are told that their post is trash and that they should just go to /r/DnD. I'm not a timid person, but I've never, as a 2 year mostly-lurker, felt comfortable posting questions in any of these DM subs because I feel like I don't have enough context and I'd be "wasting people's time." I use the discord instead and get in private convos. I don't think that's a good look for a "New DM" sub. I'd hate to see that amplified because the new DMs you are trying to help don't know enough to understand that their question is "vague" and have their questions filtered out for it.