My favorite advice here is about carrying a notebook. I’ve always advocated for beginning writers, especially, to purchase mini-notebooks and/or the cheap notebooks that are on sale during Back to School sales each year in August — I stock up on tons of them, along with looseleaf, though I never ran out because one year I went overboard, so not so much with the latter these days. It may seem counterintuitive that putting pen or pencil to paper within the constraints of an analog frame would be so soothing or conducive to creativity, but in fact, writing this way offers so many of the other elements of advice offered by others here including flow, discipline, focus, and time. Writing slowly, by hand, if you are able to, may seem less efficient, but I would argue that it improves the quality of your work and your process in ways that only make you become a better writer more quickly over time.