1) Come up with bad ideas first.
The best brainstorming sessions come when everyone in the room feels comfortable throwing out all of their ideas, regardless of whether or not they're gold. But some members on your team might be worried they'll sound stupid or uninformed if they pitch ideas that aren't well thought-out. Studies have shown people are especially apprehensive when people in positions of power are present -- this apprehension can lead to major productivity loss in brainstorming groups.
One way to loosen people up and get the ideas flowing? Start out brainstorming sessions by spending 10 minutes coming up with a bunch of bad ideas first. You might throw one out yourself first to show them what you mean. This will help you set a much more open and playful tone than a formal atmosphere would. Gerry Graf of Barton F. Graf 9000 has his team come up with 4,000 bad ideas before coming up with good ones.
Once you've spent some time sharing throwaway ideas and having a few laughs, you can refocus on brainstorming ideas that could work. And who knows: An idea that isn't so great on its own could spark some really ingenous ones that inform the direction of the rest of the meeting.
2) Break and build ideas.
One way to turn a few ideas into many is by breaking them down or building them up. If you're starting with a really general theme, try breaking it down into parts and details and seeing if other ideas branch from it. Or, you can do the opposite, and build up a more specific idea to have it cover a broader perspective.
One way to break down or build up ideas is to have each person in the room jot down two or three ideas on their own pieces of paper. Then, have them trade papers with other members of their team and build off their coworkers' ideas. You can rotate papers several times, and start a discussion based off the new ideas that emerge.
3) Play word games.
Word games can be powerful ways to help remove you from the traditional mindset that tends to produce generic, unoriginal ideas. If you're trying to get out of an idea rut, try adding a few games to your meeting to drum up some out-of-the-box thinking.
One great word exercise is creating a "word storm." To create a word storm, write down one word, and then brainstorm a whole slew of words that come to mind from that first word. Try thinking about the function of that word, its aesthetics, how it's used, metaphors that can be associated with it, and so on. Let the ideas flow naturally, and don't over think it -- this is meant to be a creative exercise.
Once you've listed out a bunch of words, group them together according to how they're related to one another. The goal? To come up with those less obvious words or phrases your audience might associate with whatever project you're working on.
