Not much more to add to the wonderful posts:
However, while not great in quantity, I think one of the most important points has been completely left out:
Don’t have ego.
An idea is just that: an idea. Particularly when brainstorming, lots of people like to say, “Oh, that won’t work because of this,” immediately. Usually because they had an idea previous that they’re defending. Ego steps into this. If someone proposes an idea, a brainstorming meeting is not the place to play “let’s shoot this idea down as much as possible.”
Assume your co-workers are smarter than you are (even if you have evidence to the contrary); if it takes you 2 seconds to figure out why their idea won’t work, perhaps there’s something you are not thinking of. Instead of saying “that won’t work because of this,” saying “Oh, great idea, how does that get beyond this?” or even, “I thought that wouldn’t work because of this?” The latter puts you into it, instead of your co-worker.
It’s subtle, but saying “that won’t work because of this” implies that the person had no idea about “this”. Saying “how does that get beyond this?” implies that the person knows about “this” and has a way to get beyond it. Implying that your coworkers are smart rather than that they’re dumb is a great way to make a safe environment for ideas.
Indeed, saying “I thought that wouldn’t work because of this?” says, “I must be dumb because you obviously have a smart idea (you wouldn’t proposed it if it was dumb), and I can’t get beyond this limitation.” This natural curiosity rather than dismissing the idea might actually lead you to learn that yes, there is a solution to “this.”
The other option, “that won’t work because of this,” if “this” is solved, ends up with a heated response of “well, ACTUALLY, ‘this’ has been solved,” instead of the more neutral “I’m glad you asked, most people think you can’t do that because of this, but it’s been solved….”
The other side of this is “Don’t take it personally.” If someone stomps all over an idea of yours, it’s about the idea. Perhaps they do not understand the idea, or perhaps you were, indeed, wrong. People are wrong sometimes; that’s OK. Don’t take it personally.