Shiv Singh, the dude who literally wrote the book on social media, (that joke never gets old) just blogged his best practices for crowdsourcing on his Going Social Now blog. The note I found most insightful within his post was the idea that you should:

“Build momentum by making the initiative part crowdsourcing, part education and part competitive game like. Many of us grew up playing lego and to this day are amateur designers and builders. We’re also inquisitive people. Tap into that by educating (in fun and light ways) participants about the product that they are designing. And not only provide them with ways to contribute but with ways to share their ideas with each other, participate in game type experiences around the core crowdsourcing initiative and gain points for every idea that’s used.”

Whole post is worth a read to anyone executing any kind of call for crowd participation in the future.