Choose a substitute by your goal: mild + tender (oyster/cremini) or deeper umami (shiitake/porcini).
Use the ratio for the form you have: fresh mushrooms usually swap 1:1, while dried porcini need only about ¼ the amount.
Adjust moisture: if the substitute releases lots of water (oyster/portobello), sauté uncovered until the pan looks drier.
Match texture timing: slice thinner for a closer tender bite; cut thicker for a meatier chew.
Taste the sauce after cooking—if it feels flat, add a small pinch of salt or a splash of mushroom soaking liquid (when using dried).