Wait until the pumpkin shows no green and the skin is hardened, like the ones you would buy in the store. Some people suggest curing them at warm temp with elevated humidity. Then wash with bleach solution and store in cool dry place away from other fruits. I skipped the curing part and just washed with bleach and stuck them in the basement. They are doing fine 2 weeks later. Only two more months to go.

google: pumpkin storage for more specifics on the topic.

Generally one waits for the skin to become hard enough that it is difficult to pierce with a fingernail. Then you pick it. With a Jack O'Lantern type pumpkin I'd leave it on the vine until the vine starts to die down. Once you pick it, you might wipe it down with a cloth dampened with some kind of disinfectant (maybe a mild soap solution). Then store it in a reasonably cool, dry place.

George
Tahlequah, OK