Walkthrough:The Legend of Zelda: Majora's Mask/Xykeb Zraliv/Pieces of Heart 1-26

This is in the order you get them in the main walkthrough.

Piece of Heart #1
Go to the road leading to Southern Swamp. Kill the Keese surrounding a tree with Deku Bubbles (or the Hero's Bow if you have it) and then climb the vines on the front. On top of the tree is a Piece of Heart.
 * Items required: Deku Mask (Hero's Bow makes it easier, however)

Piece of Heart #2
Go to North Clock Town. Near the Great Fairy's Fountain, there is a Deku Flower. Take it over a fence and down a hole. In here is a minigame that you can play. It involves using Deku Flowers to fly onto moving platforms and trying to get the rupees strewn around. If you get a perfect score every day, the Deku running the minigame will give you a Piece of Heart.
 * Items required: None

Piece of Heart #3
Go to the area right in front of the door to the top of the Clock Tower. The Piece of Heart is simply sitting there. Unless you're avoiding it, you're going to pick it up automatically when you go to fight the Skull Kid for the first time.
 * Items required: None

Piece of Heart #4
Go to North Clock Town. Climb some platforms near a slide until you get on the top of the slide itself. Then jump onto another platform and into a tree. The Piece of Heart is on the tree.
 * Items required: None, but Hylian form is required

Piece of Heart #5
Go to the snowy part of Termina field. Locate a hole with two Dodongos inside. Kill the Dodongos and a chest will appear with a Piece of Heart.
 * Items required: None

Piece of Heart #6
Go to the grassy area near the Takkuri (near the entrance to Romani Ranch). Find some butterflies, which are flying above a hole that you can't see because of the grass. Go down and fight a Peahat. When you kill it, a chest will appear with a Piece of Heart.
 * Items required: None

Piece of Heart #7
Go to West Clock Town at night on the first or second day. Use the Kamaro's Mask to dance in front of the Rosa Sisters. They will give you a Piece of Heart.
 * Items required: Kamaro's Mask

Piece of Heart #8
Go to the Swordsman's School in West Clock Town. Select the Advanced Course and jumpslash each log. If you get a perfect score, you will get a Piece of Heart.
 * Items required: None, but Hylian form is required

Piece of Heart #9
Go to the Astral Observatory and look down and to the left of the Clock Tower. A Deku will come out of Clock Town and into a hole. Then go to the hole it went to and talk to it. It will offer to sell you a Piece of Heart for 150 rupees. Say no and it will lower the offer to 100 rupees. Accept.
 * Items required: 100 rupees

Piece of Heart #10
Go to Deku Palace and, as soon as you go in, take the left passage. Avoid the guards and at the end of the area will be a Piece of Heart.
 * Items required: Deku Mask

Piece of Heart #11
Go to Woodfall, near the Owl Statue. Take Deku Flowers to the right of the temple to a large chest. Inside is a Piece of Heart.
 * Items required: Deku Mask

Piece of Heart #12
Take picture of either Tingle or the Deku King. I personally like to do Tingle (not because I like him, just because I think it adds more background to the characters involved), but it doesn't really matter. Show the picture to the man in the tourist building and he will give you a Piece of Heart.
 * Items required: Pictograph Box

Piece of Heart #13
Defeat Odolwa. Afterward, go to the tourist building and talk to Koume. She will offer to let you play a minigame. In this minigame, you will be on the boat that you can't control, and Koume will fly around carrying a target. Shoot it 30 times to receive a Piece of Heart (if you hit Koume by accident, you will lose points).
 * Items required: Hero's Bow

Piece of Heart #14
Go to East Clock Town and go to the Shooting Gallery. Get a perfect score of 50 (after getting the Quiver) for a Piece of Heart.
 * Items required: Hero's Bow

Piece of Heart #15
Go to Termina Field. There are four holes around the field that each have four Gossip Stones, with one bigger than the other three. One is near the Astral Observatory, one is near a patch of grass (not in the patch of grass) near the entrance to Romani Ranch, and the other two are on the balcony near the northern region, one of which is covered with a rock. Play the Sonata of Awakening in Deku form in front of each set of Gossip Stones for a Piece of Heart.
 * Items required: Ocarina of Time, Sonata of Awakening

Piece of Heart #16
Go to East Clock Town. Go into the building shaped like a treasure chest and talk to the woman inside in Goron form and play the minigame. Get to the end for a Piece of Heart.
 * Items required: Goron Mask

Piece of Heart #17
Go to the road leading to Southern Swamp and go into the sole building there. Play the minigame and get a perfect score (after getting the Largest Quiver) for a Piece of Heart.
 * Items required: Hero's Bow

Piece of Heart #18
Go to Termina Field and destroy a rock near the Great Bay exit. There is a hole underneath. Inside the hole, shoot the nest on the far right. Then dive down in Zora form to get the Piece of Heart that drops down.
 * Items required: Zora Mask

Piece of Heart #19
Defeat Goht. Go to the area in Mountain Village that has Tingle in it. Go into the water and sink down in Zora Form. Look for a chest, which contains a Piece of Heart.
 * Items required: Zora Mask

Piece of Heart #20
Go to the Marine Biology building and climb above a tank containing two fish. Drop a total of four fish (to be caught in bottles) inside for a Piece of Heart.
 * Items required: Bottle

Piece of Heart #21
Midway through the Pirates' Fortress, there is a room with a Piece of Heart behind a door. Destroy some barrels at the top of some stairs and press a switch. Use the Goron roll or the Bunny Hood to reach the Piece of Heart before time runs out.
 * Items required: Goron Mask or Bunny Hood

Piece of Heart #22
Go to the area with Snowhead Temple. Go back to the area preceding and it and use the Lens of Truth to find some platforms. Jump across them, then at the last one, play the Scarecrow's Song. Hookshot to him and grab the Piece of Heart.
 * Items required: Lens of Truth, Ocarina of Time, Scarecrow's Song, Hookshot

Piece of Heart #23
Go to an area in Great Bay with a bunch of ledges. Hookshot up until you reach a patch of dirt. Plant the Magic Bean, sprinkle it with water, then ride it to another ledge. Play the Scarecrow's Song and Hookshot to him to grab another Piece of Heart.
 * Items required: Magic Bean, Ocarina of Time, Scarecrow's Song, Hookshot, Bottle filled with water

Piece of Heart #24
Go to the area in Great Bay with a waterfall. Dive down in Zora form and kill a Like Like for a Piece of Heart.
 * Items required: Zora Mask

Piece of Heart #25
Go to the area in Great Bay above the waterfall with the beavers. After winning their bottle, race them both again. They will give you a Piece of Heart for winning.
 * Items required: Zora Mask

Piece of Heart #26
Go to Pinnacle Rock. Kill sea snakes until you find a seahorse. The seahorse that led you there will come. If you talk to them, they will give you a Piece of Heart.
 * Items required: Zora Mask