Discipline is something we all seek at one time or another and the answer is always the same: make yourself uncomfortable. In life there are a few things we learn from success, but there is an absolutely endless litany of things we can learn from failure. Love seems to be the same, as it strengthens after difficulty moreso than love that is never hardened by storms. Similarly our bodies gain nothing from sitting in a chair (aside from weight), but getting up and exercising to the point of discomfort outputs great gain. The same is true with discipline. If you want discipline, put yourself in situations that are not easy and your ability to remained disciplined will strengthen.
A few years ago, I had little discipline in my life. When I began cycling, it revolutionized my view of difficulty and discipline. Now, I try to push myself on a weekly basis until my lungs feel like they're going to burst and I'm going to vomit. Honestly, I hate doing it. I get freaked out just thinking about doing it. But by forcing myself to face discomfort, I have gained great fitness but moreso an appreciation and fervor for being disciplined.
Many folks cherish their sleep above all else, and nothing will pry them out of bed earlier than necessary. In an attempt to pursue discipline, I routinely get up earlier than I need to, hating every second of it. Take this morning for instance. I got up and rode 30 miles and finished before 7am. It wasn't pleasant, but it was one more log on the fire of the discipline bon fire I am trying to construct, that will ultimately benefit every single person around me! I am certainly no different than anyone else in capability. The only limiting factor is this question: how much do you want it?
How to be Disciplined: repeatedly stretch yourself to your limits becoming familiar with that discomfort, and one day you'll wake up and realize you've attained substantially more discipline than you had. It is quite simple really, but not easy.