The night before. Seriously, to get a good spot (depending upon one's definition) you need to get a low number for the tarp line. To get a number for the tarp line you must wait in the lineup entrance area the on Thursday, Friday, and Saturday nights, starting just before midnight. It seems like you need to wait until the pumper truck finishes cleaning out all of the portapotties in the whole campground before the kind folks come walking down the line handing out numbers. Low number = better choice for a prime tarp spot. High number/no number = take what you can get once you get inside. It's an extremely friendly festival, and sitting close to strangers only lasts a few minutes, as they'll be your good friends by the second set. Have fun!