Gravity is one of the many forces of the physical world working against us. It constantly pulls at us. So, pull back. Without doing so, slowly over time your skeletal frame will bend to the will of gravity. 

Routinely assess you posture while sitting, standing, walking, and conducting work or play on your phone or computer. Ask for an objective, third party assessment. Consider having a friend use a yardstick to check your alignment. When viewed from the side, the ears, shoulders, hips, knees, and ankles should form a vertical line.

Now make a conscious effort to sit more erectly, stand more erectly, and walk, work, and play more erectly. Adjust your behaviors (e.g., hold your book higher or throw your shoulders back when standing and chatting with a friend) and your environment (e.g., raise your computer screen to a level eyesight) to help improve your posture.

If you are over thirty, poor posture may already have had a deleterious impact. Efforts to correct one’s posture may seem uncomfortable at first but press on. This will take time and effort, but it is critical to quality of life, especially in the later years.