Doodling, drawing, whiteboarding flows and concepts

Don't be ashamed to be dirty and start thinking, doodling and expressing ideas well before they are mature and square-cut.
Illustration from Undraw
This section has nothing to do with DDD but has everything to do with encouraging creative processes to function and flow ideally.
Early preparation or "pre-prep" on the concept stage is something I value a lot. I feel it makes it easier to think and work and ask relevant questions.
Making something good is not about being a genius, but being able to feel comfortable in playing with the substance of the work. Getting used to it (its constraints, its properties, the stakeholders, priorities...) is therefore very important. I'm sure you might have been in many meetings where you are introduced to a new project and various angles or questions that (later) feel totally natural but didn't get a single thought aired in that initial meeting. That's why I like this pre-prep doodling, so you are gradually "getting used" to the new work.
I think it's a really valid concept to do such spitballing...
  • on paper, if you are alone, or
  • on a whiteboard, if you are with more people.
While physical media may seem ancient to some it's much more versatile, it has no real formatting restrictions, and it enables thinking/writing/doodling that is less constrained than that enforced by digital options.
At this stage, it's more about getting your mind used to the business case, any terminology you might know (or need to know!), some flow charts to describe where you might be going, etc.
When it's in the early stages I find that sometimes I need to remind folks (sometimes even myself) that these really are just drafts or rough sketches and not a full-fledged way of building something.
Personally, I think this part is really fun—just don't let this part be a massive bookend for the work you are doing but more like a creative exercise to start feeling the materials and substance of the work. As someone who knows DDD, I use this exercise as a way of also trying a tentative "first fit" for various things I encounter in the project into the "tactical" concepts of DDD, such as Entities and Domain Events. More on those later.
Picture of some of my first notes for this project.
Note: As a part of my work with building this book and its coded implementation, this is the stage in which I really for the first time started to see what the division of services might be.