Lift with your legs
You have probably hear this often enough, but how many of us do this in practice. If what you want to lift is on the floor, bend your legs as if to squat, one knee either side of the object if necessary. Keep your back straight and lift through your knees. You should feel the strain in your legs, not your back. Doing so will reduce the stressful impact on the low back, and decrease the likelihood of injury to discs, joints, and muscles. Be sure to maintain a strong back throughout the entire lift.
Keep it close
Try to almost hug the object. Keeping the object close will keep its centre of gravity close to yours so that you to do not cantilever at the hips thus causing increased pressure and strain in the lower back.
Keep your nose between your toes
This simple idea of keeping your nose between your toes will help you to stop twisting your spine as you transfer your object from one space to another. When carrying a heavy object you do not want to twist the top part of your body in a different direction to your hips and feet. Twisting in this fashion whilst carrying a heavy object is likely to put pressure on the lumbar (lower back) discs, joint and muscles.
Keep a strong core
This refers to keeping your abdominal muscles toned and strong. Before lifting your heavy object think about engaging your abdominal muscles, this is thought to have a protective action on the lower back.
Enlist a friend
When an object is too heavy and/or an awkard shape ask someone to help you move the item. Of course the same rules above should apply to both of you when lifting the object.