Identify your use-case: sandwich/char, melt-and-brown (gratin), or baking where you need structure.
Pick the substitute with the closest melt goal (Fontina/Gruyère/Swiss) or the closest flavor style (washed-rind like Reblochon).
Use the table ratio (typically 1:1 by weight for all listed options) and shred for faster, more even melt.
If the substitute is drier/harsher than tomme, add a small amount of recipe moisture (sauce, stock, or milk) to prevent grainy texture.
Taste-test at the end and adjust salt/tang in small increments—cheese substitutes often differ most there.