No time to work out?  For those busy times with work or school, find a way to get some movement into your life.  If your place of school or work is large, try walking to as many places as you can and taking the stairs, instead of using other forms of transportation.  So too if you live in a city.  Walking to the coffee shop, grocery store, or restaurant can build exercise into your schedule and you won't even think about it - you'll be too focused getting to where you have to go.