I primarily use Jupyter for prototyping: trying ideas, plotting results and sharing notebooks for others to improve on (or punch holes in). Once a piece clearly shows promise I move it into a module. While this usually means a significant rewrite I actually see it as a benefit: I can be messy in original prototyping plus a rewrite after experimentation often leads to a better code with a small time investment.
Beyond the minimal self-discipline of actually moving code into modules I still have two three-character friction points: vim and git. Pointers on addressing those appreciated!
I would love, love, love a tight vim and Jupyter integration to be able to switch, easily and frequently, between editing a set of cells in vim and in Jupyter with solid sync between them. I am perfectly OK with vim ignoring the output. And I would love to have a git mode that only checks in the changes that cause actual differences in the python code; not timestamps or the output.