You're supposed to be onstage in 12 hours, but you haven't written a single song. You've haven't met your bandmates, much less ever played with them before. And there's still the matter of naming your band.

It makes sense that they call this thing the Rock Lottery—for the musicians in it, the odds are terrible.

On the morning of Saturday, July 14, 25 of Seattle's best players—including members of Aqueduct, Say Hi to Your Mom, Radio Nationals, the Lashes, and Maktub—will meet at the not-very-rockin' hour of 10:00 a.m. to begin the city's third Rock Lottery. At a private breakfast, cocreator Chris Weber will lead a random drawing to divide the players into five bands. Each band will have one drummer; everything else is up to chance. The only sure thing at the resulting concert later that night is an experience a lot like losing your virginity—part terror, part awkwardness, and a strange desire for more, more, more.

Originally part of a series of bizarre fundraisers in the 1990s for the Good/Bad Art Collective in Denton, Texas, the Rock Lottery somehow emerged as a repeat offender. "People were freaking out, wanting me to do it again," Weber says. "People who had performed wanted to see other people do it, and musicians in the audience really wanted to do it."

Weber eventually relocated to Seattle by way of Brooklyn and is now serving as creative director at McLeod Residence. He's already re-created the lottery's success twice here in the past few years. He cites the benefit aspect as his biggest reason to keep the show going in a different city, and not just for the sake of this year's beneficiary, the Vera Project.

"Denton has these divergent scenes in a town that's so small, and they play in the same three or four clubs, yet they still don't see each other's bands," Weber says. "I was interested to see if this event would help [Seattle] in that same way of bringing different musicians together. Maybe they'll see that person's band now that they wouldn't see, and same with the audience."

It's impossible to forecast what the Rock Lottery will deliver after the bands incubate for 12 hours. Like Weber says, the lottery is "the epitome of a one-time event."

These 25 victims musicians need all the help they can get. I've seen how these things can go—who wins, who loses, and why—so I'm offering this how-not-to-crash course. And a helluva lot of luck to you.

Dust off that old tuba. Any instruments in the closet will do—who's to say your new band won't need them?

"In Seattle's first Rock Lottery, the very first band had three lead singers," Weber says. Only one of them brought an extra instrument, a Casio keyboard, but the band made the most of it. "At one point, the drummer [Chloe from Smoosh] even came out from behind the kit and did a little song-rap, so there were four singers on the song, with just lap steel."

Don't hide behind the amps. Who cares if you're not normally a songwriter? If your ad-hoc band is full of passive bass players, somebody will have to take charge. And if you need a gimmick or two—bullhorn, vinyl costume, Who-style rock opera—to work up your onstage courage, so be it.

If all else fails, bank on the band name. Middle-school notebooks are put to shame by the alumni from Rock Lotteries past. Favorites include Somos Marquee Homos, Apple Maggot Quarantine, Gee Gee Allin Alda, and Magic Johnson: The Gathering.

Say no to drugs? Weber recalls a long-ago Denton lottery band that, only hours into practice, "decided to stop and drink for the rest of the day. [Their set] was pretty much a train wreck... it was an enjoyable train wreck, but it was pretty awful." Moral of the story? Choose a designated... drummer.

Bad ideas are the best. When David Bazan and Spencer Moody wound up together at last year's lottery, the singer and the howler knew better than to give each other space on the microphone.

"Those two sharing vocal duties... that shouldn't have made sense, and yet it worked really well," Weber says.

No telling what weird pairings will come this year—maybe Damien Jurado will croon while the Suffering Fuckheads' Craig Flory blasts a sax solo, or John Ackermann of "Awesome" and Harvey Danger's Rob Knop might bump skulls during a keyboard duel. The weird, unexpected, and chaotic always make a greater impression at a Rock Lottery; bands are welcome to play it straight, but these 25 musicians will be better off taking advantage of their rare chance for sonic anarchy.

"Come with an open mind," Weber says. "There's nothing else."