Full disclaimer that this is a subjective answer which originates from my personal experience from both academic and creative writing. It may not apply to everyone reading this, but I sure hope it will help!
The way I do it is somewhat similar to the KJ method, except I skip the handwriting part altogether because transcription, in my opinion, sucks. What I do is:
I open up a new word document (dubbed lovingly the word-vomit document),
create a few headings like "personal ideas" (sometimes also adding
rough section subheadings), "literature excerpts + sources"
(classified by topic/section/however I think is suitable), and other
relevant headings I might need.
I do what needs to be done in the day, making food, doing chores,
regular human stuff etc., and whenever I have a particular idea on
how to start a paragraph in my academic work, or a random sentence I
want to use, I quickly type it down into the document, and go about
my day. Reading some papers and found an excerpt to paraphrase/use?
Copy and paste that bad boy into the word document. Do this for a
few days, and I usually end up with a substantial amount of material
to work with.
Once I believe I have enough information to work with, I start to
visualize how my current points in the word-vomit document will fit
in the big-picture. At this point, it becomes more clear to me what
is lacking, what is redundant, and I go from there. Sometimes, if
things are too messy, I'd open up another new word document and do
one more pass of reorganizing. Once I'm done with this, I'm usually
ready to start working on my main document, and everything in a word
file means easy copy-and-pasting/editing my own ideas! I've noticed
that my brain is especially intimidated when staring at a blank
document, but once I have something to work with, either to add to,
edit, or correct, it's substantially easier to manage.
When writing the main document, I try not to stress myself too much
on going section by section. Sometimes my brain itches and really
wants to work on a particular section, so I take that free
motivation and do that instead!
Again, I believe there is no "one true answer" when it comes to motivation. Some people like to plan things out and do things methodically, some prefer to let the last-minute adrenaline take over before pumping out words, and others may rely on something in-between. What I'm about to say might sound like (and probably is) a non-answer, but I think it's important to find what's right for you. Everyone is built different mentally, and sometimes it just comes down to experimenting with what works and what doesn't. Whatever you do, just try to do something, any progress in the right step is good progress, however small. :)