One of the most familiar Christmas carols is "The Twelve Days of Christmas", perhaps because of its repetition of the stanzas for each day, perhaps because of the desire to extend the joy and celebration of Christmas over more than just one day. Whatever its current status, I find it one of the most important Christmas carols we have.
The carol starts of with the singer receiving a single partridge, in a pear tree, no less. Every day, for the next 12 days, they will receive a partridge in a pear tree, along with other gifts. I find this intriguing and significant. If there were 1 thing Christians would single out as being at the core of Christmas, the birth of Jesus would probably top everyone's lists.
So, for the first day of Christmas, spend some time thinking about the 1 thing central to Christmas - One King.