Holy shit. I have just realized the key to kicking depression:

Get outside of your comfort zone (try new things), and exercise.

It sounds corny and simple, but it's fucking true. I have been depressed as fuck, and through just working out consistently (in fun ways, i.e. not sitting in a gym staring at a wall while I run on a treadmill) and keeping myself sharp with lots of different activities I've been able to elevate my mood so much. I feel like a different person.