One small thing anyone can do to stay fit is to avoid elevators and escalators and take the stairs whenever possible. Taking the stairs will obviously help tone the lower half of your body, specifically your calves, but aside from that it is also a great way to easily burn a few calories.
Circuit training is great exercise to help you drop body fat; however, the effectiveness is lost if you have periods of rest between sets. Do your best to have the equipment set-up so that you can complete one set and move on the next set quickly. You must maintain an elevated heart rate during training to get the most benefit of circuit training.