Ler here. For me, it's all about whatever coaxes out genuine, unhinged reactions, stuff that might even surprise an experienced lee. The peanut butter and chocolate of a good session for me is maximized sensitivity and a variety of techniques.
Fingertips and fingernails, not pads. You're tickling, not rubbing. Maybe it works on some lees but in my experience, your fingernails and fingertips are best.
Vary your frequency and motion and technique, don't just scribblescribblescrible constantly. Sometimes that's what's needed but I find that when the lee becomes unable to anticipate what you're going to do, that adds to the sensory overload and they're more likely to "show you who they really are" so to speak.
It's already been said but yes, explore everywhere then return to spots where you get the best reactions. The mind games you can play where the lee knows you're approaching their worst spot and you get there, give it attention, then immediately move on and they don't know when you'll come back to it (or find another one) is some of the most fun you can have with a session.
Best position for me is the classic X, armpits and inner thighs exposed to open air. Other positions might be worth trying but for tickling, this is the gold standard and most practical. Sometimes letting the lee just lay there naked with the open air on their vulnerable spots- knowing they're helplessly exposed and about to be
touched- is enough to get them going.
Favorite tool: Wartenberg wheel. Was once described by a first-time lee as "ecstasy".
Cold tools. I've found ice is worth trying but tends to get old quick because of how fast the cold dulls nerve sensation. Here's a fun ice game (usually best for returning or experienced lees): use ice to start the session with the lee fully clothed. Find the best spots, lifting or moving clothing as needed (eg hand up the shirt sleeve to get to the armpits, lower pants for waistline, etc, this game is really fun if they're wearing pajamas). Once the ice is melted, lift or unbutton their shirt, put a fresh cube in their belly button, and use your now-cold fingers to return to the worst spots. Every time the ice cube falls out of their belly button, they lose a piece of clothing, get a restraint added, etc.
Also try a can of beer or soda from the fridge rolled on the belly and ribs. Put a fork in the freezer and try that.
A good old feather is always useful but I prefer it only for between legs after the lee's been allowed to finish once or twice. David Mack seems to have perfected this technique.
Banjo picks can be worth trying.
All that said, there's no real substitute for your bare fingers used effectively.
I know this is oddly specific, but I love when a tickler focuses on a lee's sole freckle/mole/birthmark. It's like a target lol. I also like when they play with the lee's toe ring if they have one. In fact, I recently discovered the concept of removing the lee's toe ring, and actually using it as a tool to tickle their feet with. I'm only aware of two videos where that happens, but I would love to see it in more.
Dear God, yes, thank you, I've never seen anyone else mention this before. One of my favorite games is to kiss or tickle all beauty marks.