Level 1 Door Unlock
You can make the path easier in the first labyrinth you encounter. Enter this underground maze known as "Level 1" and them immediately exit. When you enter a second time, the door to the north that was previously closed will now be unlocked.
Fewer Foes
As you explore the landscape, you will encounter screens with several enemies. As you leave an area and return these enemies will respawn, but if you kill all but one enemy on a screen the rest of the creatures will not respawn the next time you pass by this area.
Defeat Gohma Easily
You will encounter the one-eyed monster Gohma in some of the labyrinths. Before you enter Gohma's room (it will always be the room one screen in front of where the triforce piece lies) equip your bow and arrow. Fire as soon as you enter the room; Gohma will be positioned directly in front of you and the arrow will strike him in the eye, killing him in one shot.
Secret Save Screen
You must have two controllers inserted into the NES for this trick to work. Pause the game by pressing "Start" on the first controller. Press "Up" and "A" simultaneously on the second controller. This will open the alternate save menu, allowing you to save your progress without dying as is normally the case.
Play Second Quest
After you defeat Ganon once, you can play a second quest. The overworld is the same, but the locations of the labyrinths and hidden items will change. You can use this cheat code to access the second quest at any time. On the game select screen menu, enter "Zelda" as your player name and you will be whisked to the second adventure.