1. Set over the course of a weekend. Allows greater breadth of attendees. Not 24 hours (which is somewhat manic) but rather a more leisurely schedule of Friday: beers/pitching/team-forming; Saturday: hacking; Sunday: polish, pitching-practice, pitches, award ceremony.
2. Strong focus/process/timetable. Ensure everyone knows the schedule and judging criteria they're hacking towards. Set out the support infrastructure and resources at the top of the weekend so people can get up to speed in the methodology of the weekend. Startup Weekend tells attendees to create a plausible startup, then links them to Lean Startup resources and hands out lots of post-its for their business-model canvases. Major League Hacking tell people to make something "cool", then feed them boxes of Red Bull and loaner-hardware. Horses for courses.
3. Experienced organisers and mentors. Have at least one person for whom this isn't their first time running a hackathon, and knows how to sort out and prepare for all the little things that can (and will) go wrong. Mentors are invaluable for setting the tone of the hackathon and guiding everyone through the event and criteria (see point 2).
4. Pizzas/generic junk food are fine (and expected!) once in a weekend. ONCE. Similarly, lots of caffeine and beer (at the beginning and end) is great for getting a buzz on, but put out plenty of water and maybe some juice/herbal teas as well. There'll be plenty of natural highs by wrap-up time, and reasonable adults won't attend if they think they're gonna feel terrible the day after (see point 1).
- Thematic hackathons provide an opportunity for hackers to learn about a new domain, and for domain specialists and otherwise interested-persons to get involved where they might not at an event specifically organised for them, but OTOH it can dissuade some hackers from attending who don't think they'd be interested. In order to resist any gimmickiness, there should already be a dialogue or narrative - either an existing community which has already expressed interest in the domain (e.g. an open data community regarding city-infrastructure), or more general hype and interest (think Startup Weekends).
And remember, it's people in a room to have fun together in a slightly unconventional way. Make sure that you build up the community and teamwork of it all the way through, look after everyone, go have beers after, and start planning the next one if people are asking for it!
It's a thematic hackathon ("Startup Weekend Immigration") happening on May 29-31 in SF. We'll be hacking on ways to make it less difficult for immigrants to achieve a better life in a new country, and we have some great speakers including the CTO of Zenefits, who struggled with visa issues himself while co-founding Zenefits.
If you know anyone who would be interested, they can use the promo code "hn" on Eventbrite to sign up for $25, which includes all meals during the weekend. (Early Bird pricing ends tonight at 11:59pm PST.)