Identify your use case: topping, cake/muffin batter, or a cooked filling/sauce (tartness and thickness are handled differently).
Choose a substitute from the list: match closest texture first (blackberries), then match sweetness/tang (cherries, strawberries + lemon).
Use the listed ratio. If your substitute is sweeter than raspberries, reduce added sugar in the recipe by about 1–2 tablespoon per cup of fruit.
If you need a smoother finish for sauces or fillings, mash thoroughly; for seedless style, strain after cooking.
Taste-test: add a squeeze of lemon for tang or a pinch of salt to boost berry flavor before serving or baking.