To secure a spot at onboard shows, it's best to book early. Some cruise lines allow you to reserve during online registration, while others offer the option to reserve directly from your stateroom TV or by visiting the box office onboard the ship. If a show is sold out, there's still a chance to get in. You can show up early and request to be put on a standby list. Typically, some people who make reservations do not show up, and the standby list is allowed in.
