The images below (all but one) are scanned from David Allen Sibley's excellent
Sibley Guide to Birds — I didn't have his permission to use the images, but my motives are academic, not mercantile...

Here's a crow on foot.

Here's a raven. The scale is about right, too: ravens are about twice the size. Notice the heavy bill, too.

This is a traditional Pacific Northwest Coast Native depiction of eagle and raven; eagle is on the left, and has a hooked bill (suitable for tearing into carcasses), while raven, on the right, has a blunt bill. He's a scavenger, and eats all manner of stuff.

Here's a raven in flight; notice the deltoid tip of the tail, how it tapers to a point? The wings do, as well, indicating a long-distance flier. Ravens often accompany herds of caribou in the north, which can take them pretty far afield.

Here's a crow in flight; notice the difference in the tail and wingtips. Short, no taper -- indicating a short-distance flier, mostly taking off and landing.
Again, the scale is pretty accurate.

Another image of ravens in flight, engaged in acrobatics, which is common. They can fly upside-down, too.

And again, notice, in this image of a raven soaring, the wedge-shaped tail.
Now you know how to tell a crow from a raven.