My depression always gets worse at this time of year too. I'm certainly not a good example today because I have been feeling extra-down. But you are right about exercise improving symptoms. Activities that are physically empowering are also emotionally empowering. It's hard to get the motivation to work out when I'm feeling deeply depressed, but I make myself drag my sorry behind through it and do end up feeling better. It might sound silly, but power poses really do work! In the short term at least, so it can help before a social interaction. I think most people get more social-phobic when we feel depressed, because actual or perceived rejection will hurt so much worse and make us question our self-worth. Getting out in the sun when weather permits helps. So does having plants in my apartment, and listening to nature sounds and classical music.

None of this is 100%, but it gets me through a day until my mood eventually lifts again.