The ability to control one's feelings and overcome one's weaknesses; the ability to pursue what one thinks is right despite temptations to abandon it.
In order to build this skill, you need to first educate yourself on what are the correct decision making skills that can improve your life and lead you to success (Our online trainers can help identify those things for you as well.) Next, you need to identify what are your internal struggles. These could be the roots to your laziness, bad-habits, and such. These problems you have with yourself can be solved one step at a time by controlling your impulses or avoiding the bad-habits entirely. This mindset will take time to adjust because you're still at the beginning of getting rid of your bad habits. Afterwards, it will become natural to you. While you do remove the negative aspects of your life, you can also implement new characteristics that will get you to improve dramatically.
Remember these important details. You have to convince yourself why you want to make these decisions with legitimate reasons or else you won't last long self-disciplining yourself. Also nobody else will be there to help you, this is your own struggles that you have to overcome it. Solving it on your own is a great feeling to know that you are competent with your goals.
Self-Discipline enables you to choose correct decision making based off of implications that can elevate your character. In other words, your thoughts and behavior will lead you to improvement and success. It also gives you the inner-strengths to overcome addictions, procrastination and laziness and to follow through whatever you do.