First, don't use much of it. When it goes to the landfill, it's a "nonrenewable resource." (How easy is it to find all those crumpled sheets in a landfill and reuse them?)
If you do use it, use it for all its worth. After the original use, wash it of course. But wash it again if it's still in good enough shape. Grease and baked on stuff will come off with hot water and a good soak.
When it's too far gone to use again for covering things, wad it up and use it as a scouring pad. You'll be surprised how well it works.