I agree totally with Flash asking for a little more information, especially if there isn't a seperate area that is cordoned off, this should be your first concern. Young children/drunk people/stupid adults will wlak right up to you and get in danger of being whacked unless you define the area and/or have safeties to help with that.
However, half an hour isn't necesarily that long, I regularly do gigs from 1-3 hours. Admittedly, I'm pretty tired after 3 hours. The way I prefer to do long gigs is to to take it slow, take my time in refuelling, stop often to let people applaud, even its something simple and talk to the crowd a lot while doing gentle movements.
A great way to stay rested and involve the crowd more is to tell them about what you are going to do next, explain whether it's easy or hard, and pretend to be scared when attempting the hard stuff.
Remember most people watching won't even notice the "technical" stuff, if you don't tell them what you are doing, just do the easy stuff.
A great finale would be for the two poi'ers to do a small set at the end, while the staffer dipss for a while and sets up for a burnoff, (the fireball thingee).
Walk between the two poi'ers, as they stop spinning and do a huge burnoff, leaving everyones equipment still going put the toys on the ground and take a (ONE ONLY) bow.
Well that's my two cents worth, its all just advice, take the good stuff leave the bad stuff but keep it safe, as nothing wrecks a performance (and fire gigs in the future too)more than yourselves or the audience getting hurt...
Good luck (you won't need it)
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Charles
http://juggling.co.nz