When you are lifting weights posture and proper body mechanics is just as important as lifting techniques. It is essential to avoid injury. Keep your head above and centered over your shoulders, shoulders centered over your hips, knees slightly bent, feet about shoulder...
Depending on your current level of strength, and individual goals, the level of intensity must be high enough that the body recognizes the need to make strength improvements. Furthermore, the intensity must be repeatedly increased, otherwise the body gets used to it...