Apologies for being nine days late, but I still wanted to make sure to come back.
As I’ve mentioned before, literally everything in this guide has helped me on my WK journey so far! But as you requested the number one thing, I’ll say it’s the recommendation of KaniWani / KameSame.
Thanks to your suggestion, I started KaniWani at the same time I started WaniKani. It was incredibly enlightening to learn about the difference between recognition and recall. KaniWani has been invaluable in helping me learn kanji, really getting the mnemonics to stick, and testing my actual ability to come up with the vocabulary or kanji on my own.
It’s strange, but sometimes I feel a greater sense of accomplishment when I get something right on KaniWani vs. when I get something right on WaniKani… haha. I think using KaniWani has completely changed my learning experience on WaniKani for the better, so I feel really grateful to have learned about it so early on!
With regards to your post a few weeks ago about rewriting the script section of the guide,
my favorite scripts are Kumi’s heatmap, rfindley’s Ultimate Timeline, and gth99’s Level Up Celebrator. The timeline helps me get a sense of how many reviews I have coming up, while the heatmap and level up/milestone celebrator (you can choose whatever picture you want 
) help me stay both organized and motivated :') Personally, I don’t use the reorder script.
A big thank you again for writing this guide and keeping us beginners in mind! I’ve really enjoyed my journey so far and am looking forward to how far I’ll be (hopefully) able to go 