The first carols were not songs, nor were they specific to Yule.

For pagan religion is preeminently danced religion.

“Carol”* originally meant a round dance (one of the first recorded uses of the word in English—from 1330—referred to a “carol of the stones,” i. e. a stone circle**), and specifically a ring-dance performed to sung rather than instrumental accompaniment. (They say that when it wasn't safe to have musical instruments at the sabbat, we danced there to songs and mouth-music instead. At the sabbat, you can't not dance.)

In fact, the carol is one of the great sacred dances of Europe.

The leader of the singing stands in the middle of the circle of dancers. This is the Lord (or Lady) of the Dance. He or she strikes up any song in 4/4 time that has a chorus and verses. The dancers join hands. During verses, they take four steps in towards center, maybe raising their hands as they do so, and four steps back, lowering their hands. Repeat. 

O the holly and the ivy,

when they are both full-grown:

of all the trees that there are in the wood,

the holly bears the crown.

 During the chorus they circle.

O the rising of the Sun,

and the running of the deer,

the singing of sweet Robin Redbreast

when merry Yule draws near.

Repeat. That's it, simple and sweet. So easy anyone can do it with little or no practice, especially if there's someone to call out directions.

Of course, there are many possible variations. During verses you can drop hands and dance in place. You can reverse the direction of circling each time. If we've got a lot of people, sometimes we'll form concentric circles. This can be immensely powerful, especially if they're circling in different directions. Everyone can sing everything, or you can alternate between solo voice (verses) and everyone (chorus). It's a immensely flexible form, deeply magical; and did I mention that it's lots of fun?

Sometimes we dance the carol with the circle of men on the inside, facing out, and the circle of women on the outside, facing in. This is a good one for Bealtaine, for obvious reasons. (Hal an Tow is the song we generally use for this, if you know it.)

Although particularly apt at Yule, with its implicit symbolism of the Wheel (the in-out movements are the spokes), you can dance the carol at any season; all you need is a dancing-ground, willing dancers, and a 4/4 song with chorus and verses.

A reporter once asked a witch, “In your religion, do you pray?”

The witch paused a moment, then smiled.

 “We dance,” she said. 

*The word is thought to derive—via French and Latin—from the same Greek word that gave us choral, “of or pertaining to a chorus.” In Classical theater, of course, the chorus danced as well as sang.

 **Þis Bretons recged about the feld, Þis karole of the stones beheld, Many time yede tham around.