What should I actually ask a group before joining my first dungeon run?

I'm coming back to the game after a long break and I think I've got the basics down again, menus, keybinds, the usual stuff. What I still don't have a feel for is group etiquette when you're the new face.

I've looked over a couple of talent build guides so I at least understand what my own class tree looks like now, so I don't feel completely lost about my own character. But when it comes to actually joining a group for the first time, I don't know what's considered normal to ask beforehand and what might come across as wasting everyone's time.

Things like whether to ask about the route they're planning, or if certain roles are expected to already know mechanics, or if it's fine to just say upfront that it's your first time there. I don't want to hold a group back, but I also don't want to just stay quiet and hope for the best.

So here's my one question: what is okay to ask a group before a run even starts, without it being seen as a bother?

The bit about saying upfront it's your first time there, just say it, nobody sane holds that against you, the only people who do are the ones you don't want in your group anyway. Asking about route is also fine, groups that get annoyed by that question usually haven't agreed on one themselves and are hiding it.

Where it gets murky is the mechanics question, because "do I need to know X" depends entirely on which dungeon and which level bracket, something like Ruins of Lordaeron plays very differently late evening with a half-asleep group than it does at peak hours with people who've run it twenty times. I don't actually know if that difference is bigger or smaller than it used to be, someone who's done more recent late-night runs there could check me on that.

My honest advice is ask the tank or whoever's leading specifically, not the whole group, less pressure on everyone and you get a straighter answer.