Double Dragon 2 is a tough game, especially if you're just starting out with it. But if you're playing by yourself, there's a way to give yourself a slight edge.

First, pick a 2-player 'B' game, so that you can hurt your partner. Then, after you've cleared the enemies away, start beating up on the prone second player.

Keep on beating him up until he's gone through all of his lives. As you're eliminating the dead weight, you'll notice that your number of remaining lives is climbing. Keep on going until you have them all

Which will definitely come in handy, trust me.