Once in life you must be told to sit straight or keep your back upright, we tend to have a very bad posture because of various reason like riding bike, injuries but one of the main reason is that you have a weak scapular and backbone muscles. I will give you some very simple but quite effective Workout. There are somethings to keep in mind before i tell you the exercise , you need to do the workout daily and you will require a Foam Roller .
Before starting do a proper warm-up. Do this regular to have better results.
1) Thoracic Extension on Foam Roller
Place the foam roller horizontally just below the scapular blade on the middle back portion. Inter lock your hand and place it behind your head, now slowly go back exhaling ,try to touch your shoulder on the ground now come up slowly inhaling and repeat this 15×2 times. While doing this don’t give a jerk to your neck, At first you might not touch your shoulder to the ground, so do it as far as possible, with every repetition calm yourself down.
2)Forearm Wall slide with Foam Roller
Stand straight near a wall, hold the foam roller to the wall and press the foam roller to the wall with your forearm. The hand should be straight and about your shoulder distance. Now contracting your core while putting pressure on the foam roller , start moving it up and down. You will feel your scapular blade activated. Do this for 15 times in 2 sets.
Basically this are a combination of 4 exercise collectively. In this you need lie down on the floor on your stomach. The letters Y T W L are the way you keep the hands. The main point is you need to activate your scapular blade by holding it and lift your arms up slowly and down. You need to do 15 reps in 2 set in each position of your hand that is Y T W L. Stop if you feel pain or discomfort.
4) The Cobra
I think some of you must know this exercise. Lie down on your stomach and place your hands besides your chest. Now push your upper body upwards, while doing this inhale ,once you are stretched hold your breath and wait in that position for some seconds than come down to starting position. While you are in stretched position you must feel a stretch on your stomach.
5) Forearm Plank
Yes a plank, it is one of the best exercise, it benefits it many ways but giving you good body posture is also one of its benefits. You need to keep arms parallel on the ground in shoulder distance and lift your body. Do not raise your hip too high or too low, keep it quite parallel to the ground. You need to do this for 1 min for 2 times, you can start from 30 sec if you are new. While doing this contract your core.