Pick the substitute that matches what you have: want the closest color and complexity? choose balsamic; want the cleanest savory tang? choose rice vinegar + soy.
Use the listed ratio as your starting point, then adjust by taste for sweetness (add 1–2 pinches sugar) or depth (add a few drops soy/salt).
If your substitute is sharper (white vinegar), start at ¾ of the amount and let the mixture sit 2–3 minutes to round the acidity.
For sauces and dressings, stir well and taste once the liquid is combined; for marinades, mix with other ingredients before adding.
When cooking, add the vinegar near the end so you preserve the tang that Chinese black vinegar is known for.