Diversify. Your body will eventually get used to your daily 30-minute walk or your weekly aerobics class. You may also start to get bored of it. Mix things up a bit. Cycle one day, walk another, jog another, go to the gym yet another. Go to different kinds of gym classes. Try different trainers. You need to work out your whole body as much as possible and you need to change your routines so that your muscles become stronger.