I’ve been playing Super Mario Bros. on the Nintendo NES for nearly 30 years. But it’s only recently that I discovered (through GoNintendo) that the game support continue.
When you have lost all your lifes and are back at the titlescreen, hold down the A-button and press Start. You will then start at the beginning of the world you died in.
It would have been nice to known this trick back in the days. There wouldn’t have been so much frustration.