Don't store in garage, the cans will rust. Store it in a closet or laundry room.

I moved my leftover paint into plastic juice bottles, like Ocean Spray bottles. I can see the color through the plastic, and if it is separating. I write with a sharpie the color name, number, and rooms used in. Store them in the laundry room cabinet, up high.
When I need to use it I shake it up until it's remixed and pour some into an old Tupperware bowl or a roller spreader.

Store your paint in a moderate temperature environment. Place paint in a properly marked plastic container that is suitable for its volume (avoid excess air). Depending on container size (i.e. a necked down bottle) place a thin layer of water (if using waterbased paints) on top of the transferred paint to mitigate drying/skinning of the paint. This small amount of water will not affect rheaology/transfer properties of the paint. Stored in the above manner you might get 10 years out of a properly formulated batch of paint.