Of the thousands of common bridge conventions that are either offensive or defensive, two common offensive bridge conventions are the "4th Suit Forcing" and the "Flannery." One of the most common defensive bridge conventions is the "Cappelletti."
In the offense "4th Suit Forcing," the player and her partner find a way to make a game contract even when the hand is incomplete. The player's partner keeps the bidding going by calling the suit that has not been mentioned in the auction, giving the player the chance to win points. The "Flannery" is an offense where the player places an opening bid of two diamonds. This allows for a minimum opening of 11 to 16 with at least four spades and five hearts. It is hard to build a defense against and can stand against most of an opponent's openers.
The "Cappelletti" bridge convention helps a player combat a strong opening "1 No-Trump" bid auction from an opposing player, creating an aggressive defense. If the player on defense has a long suit, he then bids two clubs and waits to see if his partner or his opponents partner passes. If they pass, the player calls two diamonds or makes a waiting bid, allowing his partner to call her long suit as well. If the opponent passes, the bid is reverted to the "Cappelletti" player. This defense allows for an energetic defense against one of the toughest bids to beat in bridge, and it has some variation depending on the player's hand.