Last year after carving pumpkins, I picked out about 30 seeds. Washed them, dried them, let them sit out in a dry cabinet for a month(to prevent mold), then stored them in a ziplock bag. This year we had to find a place to plant them, which took some planning, otherwise I would have started them sooner for larger pumpkins come October. Because of limited space I only used about 10 seeds, but from what I hear pumpkins are unruly and I may have more than I bargained for!
Before planting, file down the edges of the seeds (so leaves will not damage when emerging) and soak in warm water for an hour or two.