When we exercise, we must stay focused if we want to see results. In this sense, some research has discovered something surprising: when you focus on a muscle group while doing an exercise, the benefits are better in the short and long term.
There is a connection between mind and muscle that helps you improve the results of your workouts. This strategy consists of performing the exercise paying attention to the muscles you want to activate, be it your biceps, chest, back, legs, etc.
The exercises we perform activate different muscles; this is something that occurs naturally. However, depending on the routine you have, you can target a specific muscle. For example, when we do push-ups, the main muscle group is the chest, but we can also work the triceps.

If you have to stop physically, don't do it mentally
When we are injured, it is impossible to perform movements for a certain time. When this happens, we can lose muscle mass, and even strength and mobility.
To prevent this problem, it has been shown that you only need to visualize yourself performing exercises that engage the injured muscles. This action, simple as it may seem, helps you avoid losing strength.
The explanation is that when we do not activate the muscle, neither through physical nor mental contractions, the neural impulse of the unused musculature is lost. The mind is so powerful that without executing the movement, it can make us believe that we are training.

What to do if you are a beginner?
If you are a beginner athlete in weight exercises, you will benefit from using isolated exercises for each muscle group to specifically feel what is stimulated in each movement. At this stage, focus on executing the exercise well, in a controlled way, and feeling the trained muscles.
We can move a lot of loads (external) but feel nothing in the muscle (internal). In the increase of muscle mass, it is much more important to feel that the muscle works, than the weight that is lifted.