2. Determine the song category
When it comes to holiday music, songs can be put into four categories.
Religious: Songs that include lyrics about God, Jesus, Mary, Christmas, or Hanukkah. Examples could include "Silent Night," "Oh Come All Ye Faithful," "Joy To The World," and "Hanukkah, Oh Hanukkah."
Secular Tier 1: Songs that mention Christmas and/or Santa and are not religious. These include "All I Want For Christmas Is You," "The Christmas Song (Chestnuts Roasting)," "Feliz Navidad," and "Have Yourself a Merry Little Christmas."
Secular Tier 2: Songs that mention Santa, but don't mention Christmas and are not religious. Examples include "Here Comes Santa Claus," "Santa Baby," and "Santa Clause is Coming to Town."
Secular Tier 3: Songs that don't mention Christmas, Jesus, or Santa Claus and are not religious. These include "Deck The Halls," "Sleigh Ride," "Baby It's Cold Outside," and "Winter Wonderland."
You'll need to ask the event organizer regarding what type of songs are permitted. This may be dictated by the type of audience that will be present, so make sure you know this ahead of time.
Many office parties are required to keep things non-religious, so you'll want to go with secular songs that talk about holidays and the season, but you'll have to ask further as to what's acceptable to determine which tier you can be choosing from. For certain people "Santa Claus" is considered religious; they wouldn't be mistaken, since the word is actually derived from the Dutch Sinterklaas—a dialectal pronunciation of Saint Nicholas. So make sure to find out what's appropriate for the audience in attendance and chose your songs accordingly.
3. Dress appropriately
The way you're going to dress a lot of times is determined by where you'll be performing as well. If it’s a company holiday event, you might need to be more formal—guys will need to wear nice pants, shoes, and shirt, whereas ladies will need to wear a cocktail dress. Find out if small holiday accessories like festive ties or Santa hats are appropriate. If you're performing during the day at a bar on the beach, shorts, T-shirt, sunglasses can easily be part of your outfit. Ask the venue or event organizer for this information. It's also important that everyone in your band dresses accordingly, so communicate this to all your band members.
4. Prepare enough songs to fill the set + 2
Once you know how long the set is supposed to be, make sure you time your rehearsals, that way you know if you have enough songs to fill the entire slot. It's smart to have at least two additional songs prepared as a backup. If people like your show, they might ask you to play one or two more (this usually can translate into nice tips!). Plus, if you feel out the crowd and you need to swap something out on the fly, you've got options.
5. Print the setlist
If you're playing with a band, you don't want to pause between each song to announce to the players what song you're doing next. Prepare and print the setlist for each player that way everyone can stay on track during the gig.
6. Get parking info ahead of time
This may seem basic, but trust me, there's nothing more stressful than spending 20 minutes circling the block in search of a parking spot during the holidays. Find out if there's any designated parking for you and the band members. This is particularly important if you have equipment that you need to unload.
7. Public or private? Ask about event details
Ask if this is a closed or open event. Some gigs you can bring friends and family to, others, however, are private events where bringing your own guests would be frowned upon. So ask about this ahead of time. If it is a gig that's open to the public, follow up with questions about how your friends/fans can get tickets to it, and if there are any discounts they offer for family members.
8. Sheet music, iPads, or from memory
Certain clients will be really weirded out if you're on stage with your sheet music or lyrics. Others, however, will be totally cool with it. Find out ahead of time if you need to have all the music/lyrics memorized or not. Also, since the world is going digital, many performers are choosing to use tablets instead of printed sheet music/lyrics. Again, make sure that this is OK, as not every gig will find that to be appropriate.