When attending a Christmas concert, it's important to dress appropriately for the occasion. For women, a classic and elegant outfit such as a dress or a skirt with a blouse would be suitable. For men, a suit or a blazer with dress pants and a tie would be appropriate. Accessories such as jewelry or a scarf can add some extra flair to your outfit. Remember to dress in layers in case the venue is cold, and comfortable shoes are always a good idea!