In addition (and actually related to..) what Dave said about low light/night time walleye fishing, I've found that if I'm on the water when it is somewhat murkier than usual (not downright dirty, just somewhat off color), walleye will often move into the some of the feeding slots usually occupied by smallmouth when the water is clearer. The same flies mentioned above work well along with darker leech patterns and the like.
I've had my best days catching walleye more or less accidentally while fishing for bass under these conditions.