While lifting in the gym, a muscle-mind connection should always be established. This means that whatever muscle group(s) you are working, you should be thinking about the muscle moving the weight, not just about moving the weight and completing the rep.
Doing this simple thing will increase not only your intensity and focus in your workout, but primarily will build strength and size of the muscle quicker.
The mind is a powerful thing, when thinking of the muscle that is actually doing the work, and not just moving the weight, a signal is sent from the brain to send more nutrition to that muscle. Nutrition like extra red blood cells and oxygen are sent to the muscle that is being worked and thought about, and you would have to be a dummy to think that an increase of these two things wouldn’t help.
This is one trick that can help move an athlete to the next level. Always remember to keep your intensity high in the gym. There is no reason to waste time in the gym.