Lifting with bad form places a great amount of stress on your ligaments and the discs in your spine, and can lead to muscle strain. Do not lift anything that appears to be too heavy to lift on your own. Get help.
Look at the image above for guidance. If you think that you can lift an object, try to get it as close to your body as possible. While keeping a neutral spine, bend at your hips and slightly bend your knees. You do not want to fully squat the weight up. Get a good grip on the object and engage your glutes and hamstrings to take the load off your back. If an object is too heavy (more than 35 pounds), do not over exert yourself trying to lift it.
Find a tool (a hand truck, for example) or a co-worker to help you get it to where it needs to go.
If your job, or your assignment for the day requires lots of reaching, lifting, pulling, squatting, or pushing, then stretch beforehand to keep your muscles warm and to promote blood flow.