Concentration

Defined as: the action or power of focusing all one’s complete, intense mental effort, great and constant diligence. Dealing with one particular thing above all others.
The spatial property of being crowded together, a close gathering of people or things. Bringing together military forces.
The strength of a solution, removing diluting material, increase in density. Number of molecules of a substance in a given volume.

Similar: close attention/thought, attentiveness, application, industry, assiduousness, single-mindedness, absorption, engrossment, focusing, centring, centralization, direction.
Opposite: inattention, distraction
Etymology: move joined into center

Source
Concentration is the lesson 12 of the Law of success in 16 lessons. This book is the original version of Think and Grow Rich which is a watered-down version. As an example, when you buy orange juice it’s marketed at 100% pure and looking closely at the ingredients you will notice it includes water.
It’s important to remind that this in an opinion and it’s recommended to listen to the source message aligned with our current point of focus.

Self mastery
We can work on controlling and directing our thoughts to act with organized effort according to a plan with the purpose of achieving a defined goal.
It requires mental force, enthusiasm and to replace the old thinking habits. Repetition and consistency with the new thoughts, determination to resist temptations and a straight map to attain the aim.

Visualization
I recommend meditation to have peace of mind and pay more attention.
The ability of picturing what we want with imagination and in significant details is an exceptional skill to practice repeatedly.
The book “Psycho cybernetics” expands on exercises to visualize images and create movies.
The ability to stay concentrated is key to imprint the expected results and bring it to memory as real as it will be.

Believe
Faith in the process is required, the attitude has to be in accordance to the object of concentration. The book “The magic of believing” expand on the subconscious mind. Being open-minded to study the bible also helps to understand and challenge our past beliefs. It allows us to concentrate on what matters and look at it from a good perspective.

In practice
Self discipline is growing with patience, I recommend starting with time management. Concentrate on planning your day, tracking to assess where do you invest your time and reflect on optimizing for results. Think accomplishments not activities, at the end of the day when you look at yourself in the mirror be honest and check whether your actions of the day bring fruits to your purpose. Time passes and the legacy you want leave on earth is built at every breath, stay concentrated to create it in the now.
Connect with a friendly environment and use the power of mastermind to amplify this concentration.