According to G. Wallas the first stage in creative thinking is

Graham Wallas's model of the creative process (The Art of Thought, 1926) describes creative thinking as unfolding through four stages in a conventional sequence — Preparation, Incubation, Illumination, and Verification (also called Evaluation) — with each stage's work resting on groundwork already laid by the stage(s) before it, though Wallas noted the stages can overlap or recur in practice.

Preparation is the stage in which the thinker gathers information and clearly frames the problem, before any of the later mental processes can begin — so it is the stage that occurs first in the sequence.

• Incubation — Incubation is the stage of unconscious processing that follows conscious effort on a problem; it cannot open the sequence because it needs a problem that has already been taken up.

• Illumination — Illumination is the sudden emergence of an insight into conscious awareness; it depends entirely on the unconscious work that precedes it, so it comes later in the sequence, not first.

• Evaluation — Evaluation (or Verification) is the checking and refining of an idea that has already emerged; since nothing has yet been produced at the very start of the process, it belongs at the end, not the beginning.

Of the four stages, Preparation is therefore the one performed first.