Identify your goal: anti-crystallization (candy/frosting smoothness) vs. chew/viscosity (bars, glazes).
Choose the closest substitute from the grouping above and use the listed ratio (e.g., ¾:1 means use ¾ as much by volume or weight).
If the substitute is thinner than corn syrup (often agave), simmer 1–2 minutes to concentrate before mixing.
Mix into warm ingredients when possible, then let the recipe rest or chill long enough for the syrup to set.
Taste-adjust at the end: add a small pinch of salt for harsh sweetness or a touch of sugar if your substitute is less sweet than corn syrup.