Pray to the broody Gods. I have kept track and I tend to get broodies at the end of May/ early June, or mid July or mid August and once in mid October. But every BO I have ever had has done it for me.
So I think the daylight has to be right, and the broody stars need to align, but I have tried piling up some golf balls or just plain leaving some eggs till they pile up a bit and got one to go...
Always have a plan B, cause sometimes eggs don't hatch, and few day old chicks can still make it work. I am of the camp of leaving her where ever she wants to be. I have tried moving them, only to ruin it.
Do NOT put eggs under her the first few days... so been there, so done that, only to have her move, or have her not quite as committed as I thought, only to have her really settle down 4 days later, and now I am out of eggs. So do wait till you are more than sure. And mark the eggs with permanent marker. And check the nest every couple of days.
Nothing is more fun than a broody hen with chicks.
MRs K