It all depends on the audience and setting. If we're doing fire its either a fully choreographed show where we know everything that is happening, or we're doing totally improvised stuff in which case I just try to get into the flow. I try not to do any audience interaction with the fire stuff.
For busking or stage performances I have a few different sequences and themes/costumes I will use depending on the audience (so kids get a silly show with lots of laughs while at a juggling convention it gets very technical), but I very rarely have a full routine planned out in advance.
Its all to do with who you're performing to really, and it doesn't need to be stupidly in depth. For instance I did a cabaret performance for a bunch of kids recently (with 2hrs notice) that needed a TV theme, we invented 'Lottery Leonard' and I did some silly juggling with the lottery theme music on, simple and easy but does the trick!
Working hard to be a wandering hippie layabout. Ten years down, five to go!