I'm glad you asked!
-Try taking a walk during one of your breaks or lunch, at work.
-Try taking the stairs, instead of the elevator.
-Try waking up 10 minutes early and doing a morning stretch/yoga routine.
-Try standing up and moving around. while working, at your desk.
Any one of these will start you on the right track! I would say that, once you make a step toward fitness, you can reward yourself with a cupcake. However , that might defeat the purpose. ;-)