In Super Mario Bros. 3, you can earn a TON of life in the second level. In level 2, simply get the racoon tail. Then, on the part with the goombas falling from the pipe in the air, jump on each one, coming down slowly. After 8000 points… 1UP! 1UP! !1UP!
How to make this easy is simple. Let 4 or more goombas go on the ground, then, stomp on them. While stomping on them, two or three more goombas will come out of the pipe. Stomp them. When finished with this, more will come. Be sure to come down slowly!