Identify your sauce type (chunky meat/vegetable, creamy, or light oil/butter) and pick a substitute that matches it (ridged tubes for chunky; twists for creamy; toss time for light sauces).
Measure using the 1:1 ratio—then reserve a splash of pasta water before draining so the sauce emulsifies on the new shape.
Cook to package al dente, tasting 1–2 minutes early because some shapes (like rigatoni) can finish slower.
Toss the hot pasta with sauce for 30–60 seconds, adding pasta water 1–2 tablespoons at a time until it coats evenly.
If the pasta feels under-coated, add more sauce or a little pasta water rather than overcooking.