Delivery yes, but...
from what I understand, stand-up is an art form, and the starting point to being good at it is to die on stage a bunch of times. That's how you find out what works and what doesn't. Then, you refine each of those nuggets you've dug out and melt them in a BIG FUCKING POT.
Find out what hits them in the gut, where they're weak, and then exploit that shit for
Exactly... like writing, music, art, science, and pretty much everything else worth doing, first you have to suck at it a whole lot in order to get any better. You just keep sucking, and sucking, and sucking until this one time you suck a little less, and then eventually you get to a point where you hardly suck at all.
If you aren't willing to suck at it as hard as you can, you'll never give yourself a chance to get good.