By "spray paint" I assume you mean general hardware store paint that comes in an aerosolized can (like Krylon)? If so - do it outside or in the garage with the door open (as long as you don't have a pilot light in there, like for a water heater). Aerosolized liquids get EVERYWHERE. I put down cardboard or newspaper to protect the ground. Make sure the area is well ventilated, paint fumes are dangerous. And I probably shouldn't say this out loud in public, but if it's a very small, very quick spray job I probably wouldn't use a respirator, although I'm sure many would consider that to be just stupid.
I know there are loc-VOC paints out there, but I would still follow all of these rules for any aerosolized spray.
Or if you were referring to scrapbook style paints, which are perfectly safe to use indoors, I suggest getting a cardboard carton. I put the to be sprayed item in and spray away.
I also use those lovely paper bags that lss' give me. I just lay them on the table and spray. This works fine for painting smaller items and I have been able to reuse the bag as gift wrap after awhile because the excess paints make beautiful designs.