Concentration exercise.
The most important skill in terms of intellectual training is your ability to concentrate your mind, focus on a certain object, ignoring everything irrelevant. Concentration allows you to think clearly and make right assessments. The absence of irrelevant distracting thoughts gives you a feeling of lightness and freedom. This is what allows you to work fruitfully, solving complex problems and finding new details in something very familiar.
Take a comfortable sitting position, with your relaxed hands lying on your knees. Prior to that, turn off your telephone and other possible distracters. Relax. Leave your eyes half-closed. Breathe evenly and quietly. Focus on your breathing. Feel the cool air that you breathe in and the warm air that you breathe out. Feel your respiratory system. There should be no irrelevant thoughts in your head. If your attention tries to switch or any irrelevant thoughts appear in your head, try to focus on your breathing. It’s very important to free your mind of any irrelevant thoughts during the exercises. Your head should be “empty”.