To check LED Christmas lights, you should first inspect the lights for any physical damage or loose connections. Then, plug the lights into an electrical outlet and make sure they turn on. If they don't turn on, check the fuse or circuit breaker. If they do turn on, test each bulb to make sure it's working properly. If you find any bulbs that are burnt out or not functioning correctly, replace them with a new one. Additionally, you should check the lights periodically throughout the season to ensure they're still working properly.