That's a broad question.
There's dozens upon dozens of good ways to do it. Best to pick by whome you're tickling. Same with dialogue. You have to tailor it a bit to your vic.
Items? Anything you like to use. Feathers, tho traditional, don't work well for everyone. Not everyone responds to them. Try anything you can think of, and see what you like. I have used Lego bits and bottlecaps (from when they still made 16oz glass bottles), and they worked well. I've even used sticks I found on the ground. personally, my fingers are my favorite tool. But on occasion, a thin dowel sharpened in a regular pencil sharpener works for very specific types of things (under the toes is a great spot for this tool). The stem on a feather works good for it, but you can work the dowel in when they crunch up their toes.
I'd be happy to demonstrate all of this for you :evilthoughts:
CJ