It's always good to have some left over paint on hand for touch-ups or repainting down the track.
For everyday household paint, it's best to store any tins in a cool/dry area out of direct sunlight or freezing temperatures. If tins are opened, clean the lid and rim of the tin then place a piece of plastic (glad wrap is fine) over the top of the tin, then hammer on the lid firmly
Keep in mind there are paints with more in-depth storage requirements, for example, if classed as a hazardous
substance, such as epoxy paints, there are different storage requirements that must be adhered to. Always check the tin label for details.