So, you've just started exercising. Beware of overdoing it! If you work out too vigorously, too soon, you may intend to burn more calories more quickly, but in the end it will sap you of energy and could lead to an over-training injury. Start out slow and build up. Don't fall into the "if-I-don't-do-it-for-at-least-30-minutes-it-doesn't-count" trap... 10 minutes of exercise is far better than 10 minutes of being a couch potato, right?!