Use proper form. Stand with your feet hip-width apart, abdominal muscles tight, torso erect and head facing forward. Consult a book or a trainer to check your form.
Lift with slow, controlled movements.
Don't lift more than you can safely handle using proper form.
Start with a light set, then work up to heavier weights during your workout. Use enough weight that you're making an effort but not straining.
Breathe regularly and easily.
Warm up the muscles you'll use with five minutes of gentle aerobic exercises before you lift.
Cool down afterward with five minutes of slow aerobic exercises.