Good posture - often easier said than done.
For example, if you've been sitting in a slouched position for a while, the wall slide is a great way to remind yourself what good, upright posture feels like.
And this is how it works:
Stand with your back, buttocks, shoulders and head against a wall. Your feet are shoulder-width apart and slightly away from the wall. Make sure your back is not hunched, knees are slightly bent. Stretch your arms straight up so that they are also against the wall. This is your starting position.
Now let your arms sink down until the shoulder joints have reached about a 90 degree angle. Hold the position briefly and then stretch your arms straight up again.
Make sure that your elbows stay against the wall the entire time you are performing the exercise and that the rest of your body does not leave its position either.
-> Repeat the exercise about 20 times.