On this one i'm a bit like Hulan, with a slight difference.

If I'm running something for the very first time, I'll try it without watching/reading a guide. I enjoy the "holy crap" factor of not knowing exactly what's going to happen.
If it happens that I'm incapable of dealing with it, I'll thank the party and give them the option to remove me. If they're patient enough to deal with me, happy days we'll continue. If not, I'll be out of the party, go do my research on the fight as per my role, and go back in.
I don't particularly see it as a waste of other peoples' time if I want to experience the content that's new to me in game. But, I don't mind so much if i know i need to learn a bit more to beat it.