To get at least 1 extra life per stage, do this:

1. In each stage you play, get AT LEAST 10,000 points.
2. After each stage, record your password.
3. Restart the game and enter your password in.

This way, you'll get an extra life for every 10,000 points, instead of just at the 10,000 , 20,000 , and 40,000 point-mark!