Decide what you need most: smoky pepper flavor, earthy chili depth, or just heat.
Start with the ratio for your chosen substitute (e.g., 1:1 for paprika or ½:1 for cayenne).
Add in small increments, because most substitutions are either hotter (cayenne/flakes) or less complex (paprika).
If the substitute tastes one-note, fix it by adding a second spice: cumin for earthiness or a pinch of smoked paprika for smokiness.
Simmer the dish briefly (5–10 minutes) so the new spices bloom and meld with sauce or broth.