I'd like to suggest another "don't" for commentators. Don't make comments at the beginning of a hand or play based on your double dummy analysis such as "4 hearts is the normal contract and it makes" or "this hand will go down to defeat on a club lead". Personally I like to kibitz one player, such as Bob Hamman, rather than see all four hands. It allows me to compare what I would do to his actual actions. When the commentator makes a comment early in the bidding or play such as the above, it spoils what I am trying to achieve by watching just one hand.