This is what i do to get the crumbs out of my seats. Works a treat. Then use a stiff brush (hehe, stiff) then give it a vacume using the round attachment with the bristles on it mate.
I find the hoover with a pointed end picks them out with no hassle at all! For a quicker fix maybe try some duct tape, just get a small strip and go all over the seats. Picks up hairs, crumbs and any other little bits of junk!