Create the right environment
By far the most important ingredients for creative thinking are having an open mind and not being defensive or territorial about your ideas. Create a supportive environment where people feel they can generate ideas freely, without being judged or criticized.
For example, during brainstorming sessions, allow people to blurt out as many ideas as they can generate. List all ideas without commenting on them or permitting anyone else to comment on them. Express appreciation for seemingly "wacky" ideas—the more playful and imaginative, the better. Don't worry about narrowing wide-ranging ideas down to the most practical ones until everyone has finished brainstorming.
Use toys and humor to "loosen" people up and put them in a playful mood. The more relaxed people are, the easier it is for them to envision fresh possibilities and open themselves to new ideas.