Upside down, in a cool place where it can't freeze, and where it won't hurt anything if a can leaks a little.
Full cans keep better.
If you won't be able to see the bottom in it's storage location also write the info on the side of the can, or on a label you put on the side. The key to storage is keeping the air out of the can. Before closing the can, carefully wipe the 'chime' and the rim of the lid free of paint residue, especially if you didn't follow the suggestion about not wiping the brush on the lip. It keeps the rim clean while I pour the paint into a smaller container for easier handling while painting. The common advice is to close the can by putting a block of wood over the lid and tapping with a hammer, all the way around.