One of the things that typically helps to get into this mode of thinking is to take advantage of/get used to using the home row "arrow keys" (hjkl) for navigation. Instead of moving your hand to the arrow keys (or worse, all the way over to your mouse), don't leave the home row and try navigating in normal mode with hjkl.
I'm more often going to be in insert mode writing prose, but that is a different flow state. Also, even with prose it sometimes feels like you spend more time editing it than writing it.