Here are some tips to help you lift safely:
Avoid lifting or flexing before you've had the chance to warm up your muscles (especially when you first awaken or after sitting or stooping for a period of time).
To lift, stand close directly facing the object with your feet shoulder-width apart.
Squat down by bending with your knees, not your back. Imagine a fluorescent light tube strapped to your head and hips when bending. Don't "break" the tube with improper movements. Tuck your chin to help keep your spine aligned.
Slowly lift by thrusting your hips forward while straightening your legs.
Keep the object close to your body, within your power zone, between your hips and chest. Do not twist your body, if you must turn while carrying an object, reposition your feet, not your torso.
An alternative lifting technique for smaller objects is the golfer's lift. Swing one leg directly behind you. Keep your back straight while your body leans forward. Placing one hand on your thigh or a sturdy object may help.