Depends on the hen. With my broody breeds - Silkies, Cochins, Gamefowl - it's not difficult. The best way to do it is to stick a bunch of fake eggs in a nice secluded nesting box and waiting. I've actually watched an example of this happening the past several days - I got a bit lax on collecting eggs, collecting only once a day instead of twice, and within three days, one each of my Cornish and ShamoX hens started to brood.
However, it's hard to encourage a less broody breed to brood, e.g. production types and "occasionally" broody breeds. And of course no hen will brood during molting or times of stress, and few will brood during the winter.