Remember these three words anytime you are lifting: "Use Your Legs".
Never bend straight forward from the waist without bending your knees, even if you are simply picking up a piece of paper. When your knees are bent, it takes some of the strain off of your lower back.
Keep the object that you are lifting as close to your body as possible. Bend your knees and squat, keeping your back straight and your stomach muscles tight. Lift with your thigh muscles, not your back.
Move slowly and avoid sudden movements. Do not hold the load away from your body. Avoid twisting while lifting at all costs. Instead, take small steps with your feet to position your body so that it is aligned with what you are lifting or setting down.
Wearing a back belt can help support and stabilize the joints and surrounding muscles of your back but you should be aware that you may be tempted to lift more weight than usual while wearing one, since your back muscles are supported and you don't have an accurate feedback from them concerning exactly how much is too much to lift without straining your back.
When carrying luggage or other bulky objects, always try to counterbalance the load by carrying something on each side. Do not throw everything over one shoulder and lean to the side. This can cause serious structural spinal problems over an extended period of time. A backpack is ideal for balancing the load but can cause shoulder problems if it is too heavy. Always use a trolley or wheeled luggage whenever possible.