Start With Standing Straight
Modern people are hunched forward on their phones, computers, and behind the steering wheel all day long. This is the cause of a lot of neck and back pain. This posture puts our head forward of our center of gravity causing a strain our neck. It increases curve in your thoracic spine, which may prevent you from breathing properly with your diaphragm further exacerbating pain and stiffness. Evolutionarily this slumped forward posture is a defensive position and triggers the release of stress hormones leading to even more tension.
By changing your environment and being a little more conscious of your posture you can stand straighter, move better and feel good.
Your chin and neck should be back with your ears over your shoulders.
Get someone to take a picture of you from the side and see where your ears are. Your shoulders should be back over your hips.
Standing in a neutral position your thumbs should be pointing forward, externally rotating the shoulders and opening up your chest.
Your pelvic floor should be parallel to your diaphragm. You can accomplish this by tilting your pelvis posteriorly and keeping the front of your rib cage tucked down instead of flaring out.
Try holding the phone up to look at it instead of looking down at it.
Take frequent breaks from computer work and sitting.
Stand and walk more at work and at home.
Breath through your nose. This stimulates your parasympathetic nervous system (rest and digest), and activates your diaphragm.
When you walk lead with your chest not your chin.
Try corrective exercises that stretch the soft tissue that becomes tight (i.e. chest) from slumping and strengthen the tissue that become weak (i.e. back). This will not be comfortable at first but your brain and body will adapt in time and your joints, soft tissue, and even your organs will thank you down the road.