Keep you back straight but not arched. If your back is curved while you add a weighted load to any exercise, you are placing  an unhealthy strain on your back

Activate your core (trunk muscles) when performing any movement. The more stable your core, the less risk of injury.

Isolate the muscle group you are working. Make sure you can feel those muscles – and only those muscles – during an  exercise. That means, for example, if you are doing a biceps curl, the only body part that should be moving is the portion  of your arm between your hand and elbow. Your back, shoulders and legs should not get in on act. That means no swaying,  rocking or any other ways of helping that weight up.

Choose a grip when using dumbbells that feels most comfortable and natural to you. Your grip should be firm but not too  tight. Squeezing the equipment wastes valuable energy that should be exerted in the exercise.

Always control the exercise – no rapid, jerky movements, which place harmful stress on the joint ligaments. Jerky motions  actually give the weight so much impetus that it practically glides to the midpoint of the repetition, using little muscular  force to get there. As a result, muscles encounter limited resistance. Without resistance, muscles aren’t properly  challenged and may not respond as well. If you can’t lift the weight without jerking it, then it is too heavy. Try a lighter  weight. Strict style and technique are more important than the amount of weight you lift.

At the midpoint or top of the exercise, pause for a second to tense your muscles. Then lower the weight slowly again,  accentuating the negative portion of the lift. Your muscles thus get maximum stimulation from the exercise.

Breathe naturally as you exercise. Never hold your breath. Holding your breath cuts oxygen supply to the blood and, coupled  with the exertion of the lift, could cause lightheadedness or fainting.