You start from something simple and repeat this every day forming habit. Gradually it would build general self-control. For example, you start by always eating

You start from something simple and repeat this every day forming habit. Gradually it would build general self-control. For example, you start by always eating breakfast at a set time. After a few months you add going to sleep at a specific time. Once you regulate sleeping and eating you can add some exercise. After you learn how to control your physiological needs you will become more focused at work and daily life. Remember to take things slowly.