Good posture basically depends on the amount of strain you place on your supporting ligaments and muscles while standing, walking, sitting or lying down. Good posture not only adds to your appearance, but it also helps to prevent back pain and muscular pain. When you follow proper posture, you decrease the amount of wear or pressure on your joints. You are able to maintain correct alignment of your bones and joints.
The first step to good posture is to be aware of the proper posture as well as your current posture. Are you aware that your back is slumped right now? Do you notice that 1 shoulder is higher than the other is when you're standing up? Good posture means that there is good balance of the muscles on either side of your spine. When you are aware of your posture, this can lead to an automatic conscious correction on your part.
Concentrate on your position while sitting, standing and lying down. Sit on chairs with high backs and firm cushions. Your hips should be against the back of the chair, your knees either at hip level or a little lower. Your back should be supported too. When you are standing, stand with your knees slightly bent. Keep your shoulders relaxed. Your ankles, knees, hips, shoulders and ears should be in a straight line. When you are lying down or sleeping, you should lie on your back on a firm mattress.
To strengthen your muscles and help maintain good posture, do abdominal and back exercises on a regular basis. You may find it challenging to follow proper posture at first, but all it takes is a little practice. Eventually, maintaining proper posture will be easy and comfortable, and will not require conscious effort from you anymore.