Answer: Concentration is the natural state of a healthy mind. We need not improve it all. A healthy mind is naturally concentrated on the subject which it likes more. The problem with us is we like many things at a time and disturb the natural concentration of the mind.
To keep in its natural state of concentration you should give a specific goal, which you like very much in your life. That can be only one. That is called “The goal” of your life.

To achieve this Main goal, you can have subsidiary goals which will help you in achieving that main goal.
In our scriptures there are 4 main goals mentioned for any human being.

1. Artha – Wealth

2. Kama – Sense Enjoyments

3. Dharma – Righteousness

4. Moksha – God Realisation.
You can choose any one of them as your main goal of life and make other goals as subsidiary ones. To achieve any goal you should pay the price accordingly. If you select the God as your life’s goal then your life will be successful along with peace and joy. If you make Dharma (Righteousness) as your Life’s goal, then you will succeed in worldly life without any sorrow. But, if you make ‘Wealth & Sense enjoyments’ as your life’s goal, then suffering is inevitable. So be thoughtful while deciding your life’s goal. After deciding the goal learn to love that goal and Struggle consistently and systematically to achieve that goal in righteous way.
However, to keep the mind healthy in general you can observe the following disciplines in day to day life.

1. Healthy food – avoid all types of food which will make you addict and weak.

2. Physical Exercise – which suits to your temperament and makes you strong physically.

3. Reading Habit – Life of teachings of Sages and Mahatmas which gives us mental clarity.

4. Proper attitude – This life is for gaining knowledge of the Facts and not for enjoyments.

5. Naama japa – Repeating the name of the Lord whom you like very much.

6. Service – Serving the poor and needy as much as possible.

7. Sadhu Sangha – Relationship with good and noble people.