Jack-O'-Lanterns are not good "eating" pumpkins says OSU's Chowline food column. After pumpkins have been carved you have a short window of time to cook the pumpkin around 2 hours and that's when your food safety guidelines come into play.
If it's cold outside it is not safe to eat a Jack-O'-Lantern because its been sitting outside with bugs and other bacteria that can settle into the pumpkin and make you sick when you eat it; even if you have cooked or baked it. When picking a pumpkin to set outside as a carved holiday decoration then it is not good to eat, so pick one for cooking and one for carving.
You can carve any kind of pumpkin, squash or gourd but some are better choices than others. Once you select and cut a pumpkin it becomes a perishable food, additionally, if you spray the pumpkin with bleach or rub the cut flesh of the pumpkin with petroleum jelly it is not edible. Do not eat it.
Thump on a pumpkin and if it has a hollow pumpkin sound then it is probably a good pumpkin for carving. The harder the pumpkin covering the harder it is for the candle to shine through and harder it is to cut.
Pumpkins can be dipped in bleach water to help keep mold and bacteria from eating away at your pumpkin before Trick-or-Treat night. You can spray hairspray on the cut flesh of the pumpkin in place of the petroleum jelly.
One you have chosen your pumpkin, carve the lid first using a slanted angle, discard the pulp saving the pumpkin seeds for a tasty snack, and then decide what kind of face you'd like to put on your Jack-O'-Lantern. There are several templates online that can be printed off and taped to your pumpkin for tracing.