The essence of discipline is to develop good habits. If you have enough good habits, you'll stand out from others and will be more productive. Imagine if you are used to doing workouts 2 times a week, eating healthy foods, waking up early, reading a lot, etc. Your body and mind will be at top capacity every time.
So if the question is "how?" Then one step at a time, one good habit at a time should be good. Once you develop one good habit, move to another activity that will develop another good habit.
Exactly, you can't discipline your self in a particular area if you don't know how, knowing how to will put you in the right direction to discipline your self in that particular area,
After how then a regular routine of the steps involved in that area has to be practiced and adhered to steadily, and make it a routine.
Their is a way you will discipline yourself and it will become a habit and once it becomes a habit then you have done extremely well.