Think about what you do all day long vs the one exercise you do for a couple minutes daily. Which one do you think will have the greater impact on you?
If you said what you do all day long, then HOORAY! You already get it!
A lot of people are looking for a quick fix, they want that one exercise that will impact them the greatest and be guaranteed results TOMORROW, with NO PAIN TODAY! It doesn't work that way! I wish it did, trust me. I struggle with posture too.
I used to spend my college years sitting at a computer, and for 7 years after that I worked as a designer at a desk. 10 years later I am still trying to unwind all that tightness.
The greatest and most effective thing you could do for your body, is create better posture for your system. I know, it reminds you of your parents or grandparents and teachers nagging you about "standing up straight" and to "quit slouching". But they were right, in some ways.
Our bodies are so smart and will always find the path of least resistance. Bcause of this, when we are stuck standing or sitting for a long time it will figure out a way to put as little effort in from our muscles as possible. It is trying to conserve energy, and it does that because thousands of years ago that was actually necessary for survival. Needless to say when we're sitting at a desk for 8+ hours, we certainly are not at risk of overtaxing our systems. Amirite? What we are at risk of doing, is creating a lack of joint mobility, stiffness, fascial restrictions, and PAIN.
One of the most common postures is the 'ol "hanging on the ligaments" where we pop our hips forward, over arch our low back, round our shoulders and hyperextend our knees. Essentially, hanging on the front of our hips. Check out this video of a demonstration.
You can just pick a joint or tissue that might end up in pain after standing like that for days, weeks, years--anything is game! Now, check out the video to see a corrective exercise for this posture.
Once you feel where your body should be in space, then try to utilize that posture throughout the day. Find awareness and feel your body, that is my biggest piece of advice. If you can't see or feel where your body is, then we will never make great gains with our bodies and making effective changes.
Quick Tips
Ground through your feet, make sure you feel the ground
Tighten your quads (thigh muscles)
Squeeze the glutes (butt muscles)
Elongate yourself from your pelvis to your collar bones
Don't reach your head backwards
Imagine a straight line being drawn from the ankle bone > knee > hip > shoulder > ear
Other exercises to improve posture and Gait