Planning ahead can pay off big.Passengers disembark the Carnival Dream in Cozumel, Mexico.Credit: Joel Carillet/Getty ImagesKey PointsExperts recommend booking most cruises eight to 12 months ahead to secure strong fares, promotions, and wider cabin availability.Alaska, holiday, expedition, new-ship, and unusual sailings are best booked 12 to 18 months ahead or when reservations first open.Last-minute fares can drop, but savings may be offset by…