Warp to Dragon Roost Island and sail one square south to Fire Mountain. Get it marked on your chart, then get sort of close to the island and shoot an arrow at the flames spewing out of the top to stop the fire.
This starts a 5 minute timer, so quickly go onto the island and go up. If you came here by going south from Dragon Roost Island, there should be a ledge straight ahead that you can climb onto from the water. Grapple a feather from the kargaroc then kill it with the boomerang, then start heading up. When you reach a fork in the path, go right. Sidle across the ledge, keep climbing, then fall into the hole at the top.
Inside, boomerang the keese. Jump across the platforms on the lava, boomeranging more keese on the way. The lava platforms disappear, so hurry. You can kill the magtails with a parry or just make them roll up and kill them with your sword. The chest will appear. Open it to receive the Power Bracelets.
Turn around, pick up the giant stone head, and throw it wherever. Go in and kill the keese, then enter the sparkly light to go up.
Now that you have the Power Bracelets, you have access to another piece of heart. First, warp to Outset Island. Go up to the pig pen. If you put the three wandering pigs into the pen, there will be a huge black pig in the pen now. If you didn't put the pigs into the pen, read The Game Begins to find out how.
Pick up the giant pig and take him out of the pen. Be careful not to drop him or throw him into water, because it is very difficult to get him out. Carry him across to the area near the grass-cutting guy's field. Put the pig down on the place with two black spots on the ground. Scatter some all-purpose bait on the black spot on the right, and the pig will dig up a Piece of Heart.
From Outset Island, sail east to Headstone Island. Go to the little beach and use a hyoi pear. There is a Piece of Heart on top of the island as well as rupees, so fly around collecting them and return to Link to obtain the items.
Now go up the beach and pick up and throw the big stone head. Inside, stand in front of the slab and use the Wind Waker. Press right on the D-stick to switch to 6/4 time. You will learn the Earth God's Lyric and a clue to finding the next sage.