I usually start with writing a rough version (immediate expression), and refine it at a later moment (organized and structured).

I'm a little perfectionist, too, and I've found that writing a rough start helps me to create a first "overview" of the things I want to include, enabling me to add the things I've missed at that moment, or further expand on them.

Moreover, it allows me to review the initial organization and structuring of the contents, which, in turn, enables me to either further refine or overhaul it entirely.