Yoga is a great way to improve your posture, since it does great things for your spine. Practicing these postures regularly will strengthen your core muscles and help prevent back pain as well.
Stand straight, with your feet touching and your arms a little away from your sides. Lower your shoulders and bring your chin back so that your ears, shoulders, hips and ankles all form a straight line. Breathe deeply in and out for a minute.
Start in Tadasana, then exhale and bend forward from your hips. Keeping your knees straight, you can either rest your hands on the floor in front of you, grab the backs of your ankles or just cross your arms. Each time you exhale, try to reach closer to the floor. Hold the pose for 30 seconds to a minute and then slowly come upward.
Lie on the tummy with your feet together. Place your hands under your shoulders, and as you inhale, straighten your arms and lift your chest off the floor. Press your tailbone downward and feel the stretch in your neck, back and legs. Hold the pose for 10-15 breaths and then release it on an exhale.
Sit on your heels with your big toes touching and your knees about hip width apart. As you exhale, lean forward and reach your arms out in front of you. Stay in this pose for up to a few minutes and then raise yourself up slowly.
Lie on your tummy and with your arms to your sides and your forehead on the floor. Exhale and raise your arms and legs, keeping your pelvis on the floor. With your arms parallel to the floor, try to push them backwards as much as you can. Hold the asana for 30 seconds.
Start in Tadasana, then jump and spread your feet wide. Place your hands on your hips and turn your right foot outward at a 90˚ angle and your left foot inward at a 45˚ angle. Turn your chest to the right, raise your arms over your head and join your palms. Exhale and bend your right knee till it is directly over your ankle. Turn your head upward to look at your hands and hold the pose for 5 breaths. Release it and repeat for the left side.
Lie on your back with your knees bent and your feet hip-width apart. Your knees should be right above your ankles, your arms by your sides with palms facing downwards. On an inhale, lift your back off the floor, supporting your weight on your arms, feet and shoulders. Hold it for a minute and then lower yourself gently.