What sort of hens do you have? If you want broodies, be mindful that leghorns and RIRs are not chick-raising mamas. If you have silkies, BuffOs, or Cochins, leaving out eggs might work. I, however, would personally leave out golf balls. They won't go bad if it takes a while, they'll press on the breast bone (which sometimes triggers broodiness) and they don't crack and make a mess all over the place if the box gets overcrowded.
Golf balls have the additional advantage of not drawing rats.
You'll need somewhere for the broody to sit--dark, quiet, where no other sisters can bother her and lay eggs on top of the ones she already has. You may want to select eggs for lack of porousness and other deformities, or order eggs online from another breed you want.
Really, it's easiest to let the hens get broody on their own and then separate them for the duration of the setting.
You might buy some silkies, if you want chicks. They're infamous broodies. We have three, and two of them went broody this year. One was chased out by our rat problem, but the other raised twelve peeps.
EDT: Broodiness is contagious! Beware! I'd never had a broody standard hen before this past year, and all of a sudden, I had five. Out of twelve.