You should always test the weight of the load before lifting it. Then you should make sure that you are in a stable position. Always make sure you use your legs, they are your strongest muscles and minimise the pressure on your back.

When lifting from the floor you should, find a stable position, lower to the floor by bending your knees and keeping your back straight, then bring the load close to your body and use your legs to lift as you stand keep the neutral posture