Ravens almost always come into a call alone, while crows are more apt to be in murders. Ravens are also silent, crows are vocal when responding to a call. Ravens are much larger than crows. Hope this helps.
The raven's call is much deeper and raspier than the high- pitched caw that crows make...almost a croaking type sound... And they are not as vocal as crows.
When a crow is flying his tail appears to be rounded like a "C" (as the spelling of Crow). When flying a raven's tail is shaped more like a "V" (as in the spelling of raVen). Hope this helps.