Like every other month of the year there is a lot going on in Florence, but the killer event each January is Pitti Uomo. The fashion world pretty much dominates the city for the whole month, with the "beautiful people" popping up everywhere for events, parties, and of course, the major trade exhibition at the Fortezza da Basso.
Besides Pitti Uomo, there are two major exhibits/events that are closing soon:
and
January has short days, and a fair chance of rain, so visiting churches and museums should be on the top of your list, along with a hot chocolate (cioccolata calda), which you can ask for at almost any coffee bar or cafè - and don’t forget your umbrella!