After getting the Raft, you should get a heart container, then go to Dungeon 5.
Get a Heart Container
Now that you have the Raft, there is a heart container that you can get. Go to the southeast side of Hyrule, then go north until you see a small dock. Walk north onto the dock, and keep walking north until you automatically get on the Raft. When you arrive at the building, go in and get the Heart Container.
You will soon have the Bow, but you won't be able to use it unless you have arrows. Go south from where you got the heart container until you see a cave. Go in and buy Arrows for 80 rupees.
Get the Bomb Upgrade from the Previous Dungeon
After getting Arrows, if you didn't get the 100-rupee bomb upgrade from Dungeon 4, get it now if you can afford it. To get to the bomb upgrade guy from the Dungeon 4 entrance, go west, north three times, then east through the locked door, then push the middle of the east wall until you go through.
Go to Dungeon 5
Use the whistle until you are in front of a normal cave with four green trees in front. This is where Dungeon 3 was in the First Quest. Go west from here, then north, then east twice, then cross the small bridge and go north. Walk onto the dock and keep walking north to use the raft. It will take you to the entrance of Dungeon 5.
Get a Key
Go north, and be careful of the spike traps by the door. Light the room with the Blue Candle. Then go west, and once again be careful of the spike traps by the door. Kill the Like-Likes if you want a blue rupee.
Go south through the locked door. (If you don't have any keys, you will have to either buy one at a shop or go back to previous dungeons and look for some.)
Push the middle of the west wall until you go through. Use the Blue Candle to light up the room, then kill the Keese to get a key.
Get the Bow
Push the middle of the east wall until you go through. You will probably have to kill the Wizzrobes in here in order to more easily touch the blue bubble before going down the stairs. Then go down the stairs and follow the passage until you are upstairs again.
Get away from the stairs, then kill all the Wizzrobes. You can damage them while they are going through walls. Then go to the left side of the room, and push the middle block to the right. This opens the door. Go through.
You find Gohma, but you can't kill it yet because you don't have the bow. So just go south, then go down the stairs to get the bow. If you don't have arrows, you should leave the dungeon and buy them. They cost 80 rupees.
Get a Second Key
Then when you have arrows and the bow, if you need an extra key, go back and kill Gohma (if you're at the dungeon entrance, go north, west, and south, then down the stairs, then kill all the wizzrobes and go to the left side of the room and push the middle block to the right and go through the door). When Gohma is dead, take the key that appears.
Get the Map
Then go west, and go down the stairs and through the passage until you are upstairs.
Go north, then west. Light the room with the Blue Candle, then Kill the Vires to get the Map.
Get the Compass
Go north from where you got the map. Use the Blue Candle to light the room. If you touch a red bubble, you have to touch the blue one if you want to be able to use your sword again. Go north, but be careful of the spike traps at the door.
Go east and kill the Zols to get the Compass.
Go to the Dungeon Boss
Go north from where you got the compass, then go east. Kill the Manhandla to open the north door and get a blue rupee.
Go north. Go down the stairs and go through the passage until you are upstairs again.
Go west through the locked door.
Attack Gleeok's heads. When a head comes off, don't attack it, because it's invincible. Instead, hit the heads still attached to Gleeok's body. When they are all dead, take the heart container, then go north and get the Triforce Piece.