If you live in a house, chances are you have leftover paint from at least one project lurking around in your basement or garage or storage shed or somewhere.
Today's tip is forehead-slappingly simple: label your leftover paint.
You may think you'll remember that you used the desert sand in the bathroom and the bone in the laundry room, but you won't. So yes, save that paint, but label it with the name of the room or project for which you used it, and the date (according to http://www.diylife.com/, solvent based paint has a shelf-life of 15 years; latex based paint has a 10 year shelf-life). I would even tape the paint chip to the can. To free up storage space, you can transfer leftover paint to another airtight container--just be sure to label that, too.
Added bonus: if you leave your leftover paint for the new owners when you sell your house, the new owners will know which paint to use in which room for touch-ups, and when the new owners decide to repaint in EXACTLY the same colors, because they're just so perfect for the space (and/or they don't have enough artistic vision to come up with their own color combination (me, me!)), they'll know exactly what shades to buy.
For ideas to use up your leftover paint, click here. My favorite: make your own artwork (yes, we WILL, and before the year is over).
If you decide to dispose of your paint, please do so in an environmentally responsible way. Never pour paint into drains, sewers, or waterways, and don't put liquid paint in the trash. You can check here or contact your local department of environmental conservation for proper disposal methods.