if you've celebrated Christmas, you've sort of celebrated Yule, except it's on the solstice, and you stay up all night. there's different beliefs and stories, but like Lark said, it's the rebirth of the sun, so you should have a Yule fire, or at least a Yule log. the house has to be brightly lit, especially the tree. On Samhain [october 31] the Oak King [God/sun] died and the Goddess mourns. on Yule she gives birth to the Oak King [God/sun] so in the morning is when people typically have a circle to welcome the sun who will grow stronger and vanquish the Holy King, bringing spring.
has an explanation and a ritual with most of the sabbats if you wish to learn more [though Lark provided a great link] basically have your friends and family over [if they support your belief] make mulled cider, have a big potluck dinner, and bring gifts. place them under the tree as offerings to the God and Goddess, in the morning, you can exchange gifts. i know a lot of people [myself included] who do things the week leading up to Yule to prepare. go for a walk in the woods to find a log for Yule, evergreen branches, pine cones, and various other things to decorate. if you decide to make a Yule log, you can decorate and carve the log so you can place candles in it [if you don't have a fire place] myself, i go for the edible log and place candles on it during the circle we have at midnight, then we all have a piece.