Silvano Arieti wrote a book in 1976 called Creativity: The Magic Synthesis (you can get a used copy through amazon.com).
Here are his nine conditions and the reasons why:
1. Aloneness. Being alone allows the person to make contact with the self and be open to new kinds of inspiration.
2. Inactivity. Periods of time are needed to focus on inner resources and to be removed from the constraints of routine activities.
3. Daydreaming. Allows exploration of one’s fantasy life and venturing into new avenues for growth.
4. Free thinking. Allows the mind to wander in any direction without restriction and permits the similarities among remote topics or concepts to emerge.
5. State of readiness to catch similarities. One must practice recognizing similarities and resemblances across to perceptual of cognitive domains.
6. Gullibility. A willingness to suspend judgment allows one to be open to possibilities without treating them as nonsense.
7. Remembering & replaying past traumatic conflicts. Conflict can be transformed into more stable creative products.
8. Alertness. A state of awareness that permits the person to grasp the relevance of seemingly insignificant similarities.
9. Discipline. A devotion to the techniques, logic, and repetition that permit creative ideas to be realized.