Posture. Posture. Posture. Make sure that you keep your chin up and don't slouch. If you know that you are going to be standing for a long period of time, make sure that you wear comfortable shoes.
Make sure that you are getting up every 20 minutes to stretch. The type of chair you have is extremely important. It should fit you correctly so that your back touches the chair and your feet are on the floor with knees at a 90 degree angle. Try to avoid looking down at your computer screen. It should be at eye level.
Make sure you have a chair that is supportive. When you are forced to sit for a long period of time, for instance at a desk job, make sure to get up and stretch every 20 minutes. Sit with your back against the chair, feet firmly on the floor. Do not cross your legs.
Lifting objects is one of the most common ways to injure yourself. Even if it is a light object, twisting or pulling in the wrong direction when you're not stretched out can have a damaging effect on muscles and the spine. You always want to bend at the knees and avoid lifting anything you know is too heavy.
If you know that you are going to be working or playing for a while, make sure that you are adequately stretched out and warmed up. Even if it's something light like gardening or just pushing your child on a bike, it's easy to pull something if you're not warmed up.
If you're forced to use the telephone for a long period of time, a speaker or a headset is a must. By all means try to avoid cradling the phone between your neck and your shoulder as this could cause you to damage the muscles or vertebrae in that area.
Straining your neck or back while you're sleeping is a very common occurrence. We often fall asleep in strange positions where we are not supported properly or our necks are at an odd angle. Make sure that if you are going to nap or watch tv in bed, that you are in a supportive position.