Take 5. Get on your feet. Stretch. Walk. Run. Do some jumping jacks. Get your blood flowing. Get up off your rump and do something athletic. Even my great-grandma does the two step. Don’t think because you’re young and good looking that inactivity won’t catch up with you eventually. If you only have a couple of hours a day to write, move on. If you have more time, repeat steps 4 and 5. Don’t run a marathon. Do a set of sprints. You’ll force yourself to get more done.