Go Fishing
Go to the "Fishing Pond" any time after you first leave "Kokiri Village." This means that you can get the "Golden Scale" while Link, the main character, is still a child. Normally, you would not be able to receive this until Link has become an adult. Because you are obtaining this item early, you also will be able to dive deeper into the water, thus creating several opportunities to get other items early as well.
Enter the Golden Scale Contest Early
Talk to the owner of the pond and he will explain to you how fishing works. You will also learn that you may pay him 20 rupees to fish in his contest. The contest will allow you to fish for prizes. Begin fishing for the biggest prize. The owner will require your fish to weigh more than a certain amount of pounds in order to win the prize, which would normally be a piece of a heart container. The best times of day to catch a big fish are sunrise and sunset.
Cause the Golden Scale Glitch
Fish until you catch something that weighs the required amount or more. Do not return to the owner to weigh it just yet. Instead of going back to him, swim to the middle of the pond. Make sure your fairy, Navi, is not hovering over or indicating any fish and face the owner. Press and hold the "R" and "Z" buttons on your controller to lock on to him. If you find it difficult to lock onto him without fish interfering, try facing as far downward as possible.
Change the Sequence of Events
Swim back to shore, all the while holding "R" and "Z." Run to the owner and press the "A" button to talk to him, while still not letting go of the other two buttons. He will weigh the fish as usual; however, if it is large enough, he will give you the "Golden Scale" instead of the heart container. Because you broke this particular sequence in the game, you are now able to break other sequences, such as getting the heart piece from the tank in the "Lakeside Laboratory" and entering "Zora's Domain" ahead of schedule.