I plot and script everything that is significant.
Pretty much what it means would be like this,
If there are 3 key events that should happen in a
chapter than I put it in the outline
For my comic I have currently 10 planned chapters for this first part, and all are outlined in the broad sense of the word (Actual synopsis and key events that will play out). Before I start a new chapter I reference that same brief outline synopsis of the chapter then start making a more detailed outline and script for it, after that I actually start drawing the episode.
Rinse and repeat for each chapter.
However I do leave room for certain additional scenes I'd like to add that I thought of during the outlining/scripting process that I feel would enhance it in someway, this makes it also a little more fun because its not like im just smiley sticking to the planned outline entirely which I would recommend for your own story that could help with your creative process.
Not everything needs to be concrete, leave some room for changes to be made when need be