Identify your use: sprinkle/brown on top vs mix into batter or sauce for baking.
Start with the listed ratio (typically 1:1; use ¾:1 for feta to control salt and moisture).
Adjust texture: grate hard cheeses fine for smoother melting; crumble feta very small and drain 10–15 minutes.
Adjust flavor: if the substitute is sharper (pecorino/cotija), reduce salt in the recipe; if milder (parmesan/grana), add a touch more for punch.
Bake or cook as the recipe directs so the substitute can brown and develop a nutty, aged finish.