Prevent paint from drying up on the surface
A thin solid layer of paint normally builds when a paint can is halfway used. This is highly inconveniencing as the dry layer can end up mixing up with the rest of the liquid paint. Start by molding and cutting a round piece of aluminum foil.
Drop it on the surface of the used paint. Blow in some carbon monoxide into the can before closing it up with its lid. This process eliminates oxygen and prevents the surface from drying up. Discover how to pick the correct paint brush for your work.