Identify the role agave plays: sweetener only (go neutral), moisture/binding (match stickiness), or caramel/browning (choose a deeper syrup).
Use the ratio for the substitute you picked (use 1:1 for most, and use ¾:1 for corn/golden syrup).
If your batter/dough looks thinner than expected, reduce the substitute by 1–2 teaspoons per ½ cup agave and rely on the existing dry ingredients.
If your recipe needs cleaner flavor, pick simple syrup; if it needs rich browning, pick honey, maple, or brown-sugar syrup.
Taste and adjust after mixing: add a small pinch of salt to balance sweetness or a few teaspoons of water to loosen if needed.