Identify your use: cocktails (best with liqueurs) vs. baking (best with juice/syrup or berry preserves).
Choose the closest substitute from the table, using the listed ratio as your starting point.
If your substitute is thicker (jam, molasses), loosen it with a teaspoon of water so it disperses evenly in batter or sauce.
If your substitute is sharper or less sweet than cassis, balance with a pinch of sugar (or honey) before adding to the recipe.
Taste and adjust at the end: add a tiny amount of lemon juice for brightness or a touch more sweet syrup for roundness.