Breathing: Do not hold your breath while resistance training. Instead, exhale or breathe out while pushing or pulling the weight up or out and inhale or breathe in while letting the weight down or in, slowly returning it to its original position. To maintain correct posture, "think tall".
Spotting: While lifting heavy weights, a bystander should be present to assist if the person lifting is unable to finish a lift or should need medical attention.
Full Range of Motion (ROM): To develop strength throughout a joint's full ROM, training must be performed through the full range of motion.
Proper technique: Follow instructions from a trained professional; without proper technique, injury is more likely to occur. Correct posture is key to proper technique.