I've actually been going back as well recently!
The most important things in Trial of the Fool for me are enemy spawn points and being comfortable moving around with charged nail arts. At some point I changed my entire control scheme purely so I could use everything independently: keeping attack charged, jumping and dashing. There's going to be a lengthy no-floor section where you'll need to do a lot of continuous wall jumping and with the default control scheme, I found it incredibly hard to do that reliably while keeping attack charged. So make sure you find something you're comfortable with.
You'll want to be able to quickly finish off enemies with great slash right as they spawn, especially Primal Aspids (feck them!). Nailmaster's Glory is a fantastic charm for just one notch, use it. Unbreakable Strength is a no brainer and I personally always include Quick Slash as well. Some people like to rely on Hiveblood for healing in the no-floor phase, but I personally dislike that strategy. Four notches is too expensive and you're better off killing the enemies as quickly as possible.
My loadout (IIRC, it's been a while):
- Unbreakable Strength: duh. Make sure it's unbreakable and not fragile, we're not in the dream world like the pantheons
- Quick Slash: it's not an absolute must, as you'll be doing a lot of damage with nail arts. Can be replaced by Mark of Pride or Shaman Stone for example, or perhaps even a combination like Soul Catcher/Spell Twister + Dream Wielder
- Quick Focus: the quick heals cannot be underestimated
- Nailmaster's Glory: a must
- Grubsong: you'll be taking damage so getting some soul for healing in return is always good
Obviously this relies on having all available charm notches. If you don't have them, get them. Goes without saying you'll want pure nail and max masks and soul vessels.
After the no-floor section (it will take you a while to reach this point, I'd expect), don't panic. There will be a steady onslaught for a while but at some point, you'll be getting favourable enemy combinations and you'll be able to leave just one slow moving enemy alive. Abuse this situation to dream nail that enemy. Build up full masks and soul ahead of the boss that way. Dream Wielder makes this part easier which is why I've included it as a potential charm replacement, but it's not necessary. Once you reach the boss, if you're having trouble with it (I did initially), you'll be able to practice it in the Hall of Gods.
And that's pretty much all I've got at this point. Practice, memorize the rounds, know when it's safe to heal and try not to lose your mind over the no-floor section.