Potatoes need a lot of light if you want a good harvest, so choose the position of your container wisely. Make sure there are holes in the bottom for drainage, and line the bottom with stones or a similar medium.
Fill the container to about a third of the way up with compost (you’ll add more as the plants grow) and space the spuds about six inches apart, leaving a good gap to the edges of the container. Cover with another couple of inches of compost, and add more every time the plants reach about six inches above the surface.
Water regularly and within two to three months you should be able to dip into the container and pull out your first spuds.