First, decant well in advance of when you'll need it. The paint needs time to degass or, to let the propellant escape. I use a straw. Run a piece of masking tape around the back of the nozzle on the can, hold the straw against the front of the nozzle and push the ends of the tape against and around the straw to hold it in place. Then just spray through the straw and collect the paint in a jar or bottle. I usually let it set till the next day uncovered so the aerosol propellant can gas out. Whatever you do, do NOT tighten the lid on the jar or bottle and shake! hehe Because if you do, when you loosen the top paint will go everywhere. After I've let the paint set for a while I stir it, gently. If it produces bubbles or the bottle/jar cools to the touch as you stir it the paint isn't ready to use yet. If you need some decanted paint in a hurry then you can stir it until it stops bubbling or chilling. Once you get to that point it's useable. I guess it depends on what airbrush you're using (tip and needle size) but I always end up thinning it before use. Sometimes a lot.
Tony