Go to Al's Penthouse and get the Cosmic Shield at the beginning of the level. Then, go to the fire place and get the extra life. Exit the level repeat this as many times as needed.

Begin game play in the first level and collect the extra life in the crib. Exit the level, re-enter, and collect the life again. This can be done any time during the game, as many times as needed.

Go to the market place in Alley and Gullies and pass the balloon maker. Then, jump into the water where you find a duck. You should go underwater and see a small tunnel. Follow its twist and turns to find a hidden life. Repeatedly collect this to get may extra lives.