[shuzchen]

In my experience (at various hackathons, global game jams and startup weekends), the tactic that's given me most success is to be very strict about what features to implement, and to keep any unfamiliar technologies at a minimum. When you only have so much time, don't waste it writing profile settings pages (why even have auth at all? everyone just types in a username and they're logged in as that person now!), don't waste time dealing with any browser compatibility (just program for chrome, or whatever tablet you're going to demo on). There are so many things that I've seen other people mess around with that just wastes your time and energy.

Regarding unfamiliar technologies, choose a stack you're used to (that way, you don't waste time debugging/googling how to do something) and use whatever helps you get things done fast. If anything, have one unknown thing in the mix so you can take advantage of the learning opportunity. Just make sure that thing is necessary for the product you're working on of course - for example, use mongodb's geospatial indexes for that geo-aware app, or try out d3 for those nifty interactive charts, or use websockets/zeromq for a real-time system.