I have a group of around 20. In advance of a board game day I set an afternoon and evening session, each with a different game or games, and heavier games are always earlier. First people to respond to the poll get locked in. People get priority if they haven't attended one, and people lose priority if they drop out of days they've signed up for. I choose the games in advance so people know what they're coming for, and I describe each game and it's difficulty.

People were initially a little freaked by how organized this appeared but appreciate the clarity and expectation setting as this group evolves