One of the reasons for poor posture is a lack of tone in the stomach muscles. Increasing strength in your stomach will give you greater core strength and improve your posture. Go into your bedroom and lay down on the floor next to your bed. Put your feet on top of the bed and push your buttocks toward the bed frame. Put your hands behind your head and lift up from your stomach about 10 inches. Come back down to the floor and repeat 20 times. Take a 30-second break and repeat the set.
This should be done on weight-lifting bench. Lay down on your back and use two 10 lb. weights in each. Keep the weight at shoulder height and lift straight up. You will increase your core strength by balancing the weights as you lift them. Do 10 lifts, take a 30-second break and repeat the set.
Exercise Ball Roll
Place your stomach on an exercise ball. Put your hands on the size of the exercise ball and roll towards your head. When you get to the point where your neck is over the center of the exercise ball, roll back to your midsection. Repeat this 10 times.