So there's a couple scenarios my group uses. For system, that's the GMs call. Since that's usually me, I've told them if anyone else feels like running something I have no interest in running, I will happily be a player in whatever anyone else wants to run.
For campaigns, it's usually been the GM saying "I want to run this, here's the gist of it" and so far that's been fine. I picked our current PF2 AP (Abomination Vaults) largely because a couple people in the group had expressed interest in a dungeon crawl like Dungeon of the Mad Mage so AV seemed like a good way to switch systems and give them the campaign concept they want. Since the AP runs to 11 and they wanted to play to 20, I offered the 2 existing APs that go from 11-20 and they picked Stolen Fate so that's next. Whenever it is we're done with that, I'll offer up a few different APs I'd enjoy running and let them pick whatever they like. If for whatever reason they don't like any of the options, I'll probably ask what they'd want me to run.
For our Call of Cthulhu one shot games, I pick a scenario and send out a text to our group saying "I want to run a CoC game on this date, who's in?" and go from there. I don't give them any hints on what it is or what it's about, they trust I know their tastes and I picked it because I thought they'd enjoy it. If it sucks, we're out a few hours of time. No big deal.
For campaigns, it's usually been the GM saying "I want to run this, here's the gist of it" and so far that's been fine. I picked our current PF2 AP (Abomination Vaults) largely because a couple people in the group had expressed interest in a dungeon crawl like Dungeon of the Mad Mage so AV seemed like a good way to switch systems and give them the campaign concept they want. Since the AP runs to 11 and they wanted to play to 20, I offered the 2 existing APs that go from 11-20 and they picked Stolen Fate so that's next. Whenever it is we're done with that, I'll offer up a few different APs I'd enjoy running and let them pick whatever they like. If for whatever reason they don't like any of the options, I'll probably ask what they'd want me to run.
For our Call of Cthulhu one shot games, I pick a scenario and send out a text to our group saying "I want to run a CoC game on this date, who's in?" and go from there. I don't give them any hints on what it is or what it's about, they trust I know their tastes and I picked it because I thought they'd enjoy it. If it sucks, we're out a few hours of time. No big deal.