Just throw out a collection of random facts, rumors, characters, and hooks. The players will then come up with a theory to connect it all that will likely be more entertaining than anything I could have thought of ... and the campaign goes off in that direction.
It's even better when they come up with a great idea, then reject it ... 'cause you can select that theory to be true, and later they smack themselves 'cause they thought of the solution and threw it out!
and
I fear I would not have the requisite with-it-ness to pull this off successfully.
I started using this technique in 1991- it worked so well I kicked myself for not trying it before.
I was running a HERO Superheroes campaign set in the campaign world set up in the game Space: 1889 (good gameworld, BTW). Once the PCs came together in a cohesive group- as agents of G.A.I.A. (a global police agency where the "00" agents were supers), every session, I'd hand out the agency's internal memo. Each memo had "news of the world" as well as a recap of the team's exploits (as composed by a rah-rah, quas-jingoistic in-house reporter..."Good going, chaps!"). The stuff in the "news" section was full of gossip, rumors, news, and so forth- all plot hooks and echoes of PC background tie-ins.
After the session started, I'd post the memo on the game group's cork-board, and everyone could read it during cutaways, food breaks, or even other times between sessions.
Invariably, the players would openly speculate about the memo's content. I'd just sit there listening to them gossip and let them supply me with PILES of ideas and tangents.
After writing the initial 3 adventures myself, the players supplied every single plot, either directly or in the negative- IOW, I wrote something askew of their speculations.
Worked great for years, until I moved away. Nobody suspected a thing...at least, nobody said anything to me about it.
Since then, I've done the same with FRPGs with postings on the town message poles in the square, etc., and E-mail makes it easier to post the memos to the whole group AND watch them speculate.