Rule 4 of 27 · Chapter I — Before You Cook
Prep in the order the dish will need it
Why this rule exists
There is a right sequence to preparation, and it is dictated by the cooking, not by the recipe's ingredient list. The thing that goes in first, or takes longest, should be ready first; the delicate garnish can wait. Chop the onion before the herbs, because the onion cooks for ten minutes and the herbs go in at the end. Get the water heating while you prep, because it takes time and asks nothing of you. Prepping in cooking order means that when the heat comes on, everything arrives at the pan exactly when it is wanted, and nothing sits around oxidizing, wilting, or warming when it should be cold. It is the difference between a relay handed off smoothly and a pile-up at the stove.
In practice
Before you pick up the knife, decide the order: what cooks longest, what goes in first, what must be freshest at the end. Start anything that takes time on its own, a pot coming to a boil, an oven preheating, a marinade sitting. Prep the sturdy, early ingredients first and the fragile, last-minute ones last, so herbs and citrus stay bright. Keep like tasks together, cutting everything that needs the same knife action in one pass. When you finish prepping, the ingredients should be lined up left to right in the order they enter the pan.
When it doesn't apply
For slow, forgiving dishes the order barely matters, since there is time to catch anything you left late. And some ingredients must be cut at the last second regardless of sequence, like an avocado or a cut apple that browns. Sequence serves the cooking; where the cooking is relaxed, so is the sequence.