By far the most common mistake people make when lifting any object is not using proper technique.
But what is proper lifting technique? Lifting anything, especially heavy objects, can generally be broken down into 3 parts.
1) Bend at the knees to grasp the object.
2) Lift using a combination of legs and back muscles.
3) Avoid any twisting movements while lifting. This applies shearing forces to the lower back which greatly increases the chances of disc and joint injuries.
Often times simply avoiding point #3 is sufficient to greatly reduce the odds of injury. I also suggest regular chiropractic adjustments to address any areas of the spine that are misaligned because this too increases the odds of injury.