I heard of a house rule that I really like. It stipulates that players that kill another player before that player had 1 turn to play in the game (if Jail skipped a turn, this counts as that player not having had a turn to play yet) have to discard all their cards in hand and in play.
BANG! can be a long game and it is lame when you get destroyed first round. I know this has happened to me several times, and I think this house rule is a good solution.