The idea comes from Satya Robyn and Kaspalita Thompson who began the River of Stones a few years ago which involved writing to capture a fully-engaged moment. I thoroughly enjoyed participating in that and wrote a small stone every day during January, 2012 (and in fact continued for the rest of the year). I still write them occasionally and you can see them at my other blog www.pausingforsmallstones.blogspot.com.
Satya and Kaspalita write -
"You might want to share an old photo of your dog, a quote you’ve found or a story you’ve heard. You might want to write a few sentences about something that you appreciated during the day. It doesn’t matter what – just anything that makes you smile or brings a little burst of joy."
You can find out more information at http://www.writingourwayhome.com/31-days/31-days-of-joy/. There's also the option of expanding the experience and receiving an email each day as well as other goodies.
To join in with Joyful January you post an image, a few words, share a quote or something that brings you joy and share on facebook, twitter, instagram etc with the hashtag #joyfuljan. I'm sure it will be great fun and inspiration looking through the images and words shared.