I batten down the hatches and wait for my brain to recognize spring. When I can rouse myself, I go for a walk. I try to fight the carb cravings so my brain won't get further dorked up. By around February, the cravings start to take over. I'm particularly carb-sensitive, so I slog through February and March.
I used to use a lightbox, but it hurt my eyes, wasted my time (I couldn't do anything for half an hour while I sat there and squinted), and didn't do much for me. Lightboxes do help some people, so they are worth investigating.
I used to live in a house with a big sliding glass door in the master bedroom. I'd wake up, fix a cup of coffee, and work in bed with the glass door completely uncovered while the natural light streamed in. It was better than a lightbox. Unfortunately, I don't have this option in my current digs.