Just reiterating much of what has been said above.
Do not store your seed potatoes in the dark.
Lay them out, so they do not touch each other and allow to chit in the light and somewhere dry and cool.
If they have grown chits already and they are long and spindly and of a white or light pink colour, just carefully knock them off. They will grow back plenty of new chits during their chitting period.
See if you can get hold of some spare egg boxes, its the best way to chit potatoes, as it allows the air to flow around them nicely, keeps them separate and stops any dampness, that can happen if stored in plastic trays.