WORK ON YOUR STRENGTH. Hit the gym, or, better yet, dust off those kettlebells you got last Christmas and start swinging. This is also a good time to start or advance your grip training. It's all there for you, grappler. Get strong.
WORK ON YOUR STAMINA. It's true there is no substitute for time on the mat to improve your cardio for jiu jitz, but running or other cardio blasting exercises are pretty decent substitutes. You could just jog in place or run in circles in your apartment, but we suggest some of Coach Steve Maxwell's exercises, like this:
WORK ON YOUR MOBILITY/FLEXIBILITY. This is my personal weakness. Lots to do here, grapplers. Exercises and workouts abound. Here's one of my favorite Steve Cotter videos to help motivate you (and me):
WORK ON YOUR GAME. YouTube is your friend, grappler. Do some research and expand your knowledge. Next thing you know, you'll be working over black belts with your Internet-learned tornado guard sweeps and intricate Marcelo Garcia set-ups. [NOTE: this will not work, but keep trying.]
SPEND TIME WITH FAMILY/LOVED ONES. We're just kidding about this one. Seriously though, go work on that other stuff. You're family will be around in-between your workouts.