In order to get the most benefit from this little competition, it will help to keep these two things in mind and apply them:
1) Move more
2) Eat/drink fewer calories
Moving more might simply mean to lift yourself up and down 2 or three extra time each time you need to get up. It might mean adding 5 or 10 minutes to your workout routine. Whatever you do, to make sure you are a winner in this competition, move more.
Eating/drinking fewer calories is also going to be different for different people. For some it might mean cutting out one flavored beverage. For others it will mean avoiding an entire category of junk food.
Just start with one change for each of these two areas and you'll begin to see results.