I think people who struggle with self-discipline often have a choice - to continue practicing the way they are used to, keep doing what they are doing and keep getting the same results. Another choice would be to change inefficient practicing habits and start working on disciplining oneself.
Lack of self-discipline often arises because we as humans have love for things that are new. That's where so-called "shiny object syndrome" appears in your practice. This could be in the form of a new method, new technique, new piece etc.
You might think that the new practice method is going to get you better results. (Remember these new, easy, fast, and simple shortcuts dishonest marketers are promoting - like to learn to play organ confidently in 2 hours?). Shiny object might also be when you become bored with some challenging piece and start looking for something new.
Of course, we need some variety in our practice - there is no question about it. The days when a practitioner of martial arts would learn just one form or kata for 5 years are long gone. The same is true in organ practice - we need something exciting to keep our motivation up and to push through difficult days.
That's why the process of goal-setting is so important here. If you could write down a really exciting specific goal with a date, plan of action and daily steps, then all you need to do is simply stick to the plan.
One thing in particular is helpful to me in terms of self-discipline is the habit of performing in public. If I can arrange a date for the piece or pieces which I'm working on to play in a public setting (church service, recital or even for my friends or family), then I'm so much more likely to keep myself on track.
Then it would be much easier for me to stay motivated and self-disciplined throughout the long weeks or even months of solo practice because I would have an obligation to prepare well. This would prevent me from losing my focus and become a victim of "shiny object syndrome".
Do you have some tips and techniques which you use personally in your practice which help you discipline yourself? If so, please share them in the comment section below.