I don't think there is anything else, save the absolute necessities, that I would have done every day for the past three years. Even looking back one year, such essential things like morning coffee hasn't been an everyday things. I'm sure I have skipped it once or twice this year alone.
So how is it possible to keep doing something that requires conscious effort and creativity for such a long time? We are all different, so I don't have a definitive answer that would work for everyone. All I'm saying that they have worked for me.
One day at the time: there is no point focusing on some distant milestones. Just keep writing every day and you will be amazed how fast those milestones pass by.
Determination: it's your choice. You can quit any day you want. You don't have to write. You just need to make the decision to keep writing every single day.
Not giving a fuck: don't aim for perfection. Mistakes are ok. It doesn't matter what others thing about your texts, both grammatically and contextually. Just keep writing whatever comes to your mind. It's ok to write complete nonsense every now and then.
Those are the major factors I have identified during these three years that have kept me going.