Decide what you need soy sauce to do: salty umami, dark color, or a sweet-savory balance for a sauce/glaze.
Start with the ratio in the quick-reference list; use full 1:1 for tamari and coconut aminos, and reduced ratios for stronger options.
If your substitute is stronger (fish sauce, Worcestershire), dilute with a few teaspoons of water and taste before adding more.
If your substitute tastes flat, add a tiny pinch of sugar (for bitterness) or a few drops of acid (vinegar or lemon) to round it out.
For glazes and marinades, let the mixture sit 3–5 minutes so the flavors blend, then adjust salt at the end.