You can marinate flanken ribs with a dry rub or a liquid based marinade. For this recipe, a dry rub was used. To do this, wash and pat dry the flaken ribs with paper towels. Place the ribs in a ziploc bag then add a generous amount of dry rub, kosher salt and black pepper, release the air from the ziploc bag and seal it. Move the ribs around until they're well coated with the dry rub and allow the ribs to marinade on the countertop for at least 20 minutes or in the fridge up to 24 hours before grilling.