My preparation...
KITS - I save all of my kits by designer, so when MOC is rolling around, I pull out all kits by TLP designers (and all TLP collab kits) and move them to a separate folder. I restrict myself to pulling from that folder only during MOC. After getting all of the designer's kits moved, I then painstakingly go through each kit to make sure that it is still in the store. I have a folder titled "_not in store" that I move all the non-store kits into. That way I know those are not my go-to kits, but I can pull from there if necessary, remembering to keep it under 25%

PHOTOS - One year (I think it was 2017), I wanted to challenge myself to pull pictures exclusively from my Thailand trip. With the exception of 2 layouts/challenges, I was able to do the entire MOC around those pictures! I'm hoping to try to repeat that with pictures from another trip or specific time/event this year as that cut my time down significantly. Instead of searching through my plethora of photos, I had one folder that I stuck to and made the pictures that were in there work with the challenge.
ORGANIZATION - At the beginning of MOC, I start a Word document that I keep on my desktop and check/update every day. I keep the rules at the very top as a reminder (thankfully I think I'm pretty familiar with them by the 7th go-round). I then list the challenges by day, title and type -- HUGE thank you to
@AnneofAlamo for the running list that she keeps faithfully every year

That list is on its own page at the beginning of the document. I then copy and paste each the challenge details when they are posted so I can refer back while scrapping. Underneath the challenge details, I keep a running tally of everything that I use on the layout so that I can just copy and paste that when I post my layout. Finally, I copy my journaling into the Word document for each layout so that it serves as a spell check and word count when necessary. When I fully complete a layout, I will change the font color for that day so I can see at a quick scroll which challenges I am still working on or need to do.
I'm sure this seems like a lot

but I promise you, it keeps me organized and accountable. I'm a visual person and while I may not be writing a list down with pen and paper, the color change of the font is just as satisfying as checking a box or crossing out a line.