Since the mold absorbs water, if you want to get a good pour don't let the mold too wet. One excellent indication is how heavy it is because the thing is waterlogged. Sitting it empty in your kiln room is one way to get it dry. DO NOT cook the thing! But a hot dry environment is the best way to keep your molds useable.
I wouldn't pour in the same mold more than three times before letting it dry up some. If you pour too much at a time, you lose the fine detail because the plaster deteriorated. If it's a very popular mold, try getting two.