After getting bombs, rupees, the Blue Candle, more rupees, and the Blue Ring, you should go to Dungeon 1 in the Second Quest.
Get the Boomerang
Go east and kill the Goriyas to get the Boomerang.
Get a Key
Go west, then north, then kill the Goriyas to get a key.
Optional: Compass, Bombs, Map, Rupees
Go north and kill the Stalfos (which now shoot sword beams) to get the Compass. Go north and kill the Goriyas to get bombs. Go north and kill the Gels to get a blue rupee. Unlock the east door and go through, then put a bomb in Dodongo's path to make it eat it, then repeat until Dodongo dies. Then go south to get the Map. Then go north, west, and south three times.
Get a Second Key
Bomb the middle of the east wall and go through the hole. Kill all the Keese, then push the leftmost block up or down, and go down the stairs. Follow the passage until you are upstairs again.
Touch the wall to make Wallmasters come out. Kill them to get a key.
Go to the Dungeon Boss
Go west through the locked door. Then bomb the middle of the north wall and go through.
Hit Aquamentus's horn until it dies. Then get the heart container and go east to get the Triforce Piece.