Needed Items
You must wear the Goron mask several times to get through Snowhead Temple. Only Goron Link can push the massive Majora blocks throughout the dungeon -- including the one blocking the entrance -- and you can only withstand the lava pits and roll across the ice bridges in this form. The Great Fairy mask can also help to retrieve fairies you can't reach otherwise. The Bunny Hood is needed in the switch room, and the Lens of Truth will help find hidden ledges and hidden fairy locations. You'll also need lots of arrows, and remember to bomb all cracked walls.
Switch Room
In the room with the colored switches, become Goron Link and have the Bunny Hood ready. Hit the circular yellow switch and you'll pop up one switch across the gap and another blocking the door. Run and jump over to this switch. Pound on the green switch first, then hit the new yellow switch to drop to the bottom of the gap. You have a limited time -- equip the Bunny Hood, run and climb over the green switch at the door and jump to the door before the switch comes back up. If the White Boes are a problem, defeat them all and start over.
Mini-Boss Wizzrobe
The Wizzrobe shoots ice spells that freeze you, and you'll also freeze if you touch the ice patches he causes. He disappears if you approach him, so use your bow and arrows, firing before he shoots an ice spell so you can get out of the way. Once you hit Wizzrobe three times, he hides in one of the four blocks in the room, with fakes appearing in the other three. The fakes dance around their blocks but the real one always stays put; shoot that one. Defeating Wizzrobe gets you the treasure of the Snowhead Temple: the Fire Arrows.
Fire Arrows
The Fire Arrows allow you to melt the ice in the room; this includes the freezard monsters, the ice-encased Deku flower you need to glide across to the other flowers, and the frozen Majora blocks. They are also handy when you must face Wizzrobe a second time to get the Boss Key. Use the same strategy with the blocks you used before, and he'll go down quickly with these arrows, Once you have the Boss Key, you can enter the big door in the dungeon to face the boss.
Goht
You can defeat the Snowhead boss, Goht, one of two ways. He's vulnerable to the Fire Arrows, so stay in the alcove near the room's entrance and shoot Goht when he appears. You may not have enough arrows to finish him off this way, though. You can also use your Goron form. Roll around until you sprout spikes and then run over and pound Goht. A good method is to leap up, hit him in the rear, and hit him a few more times while he's down. You'll need to swerve to miss the three bolts he'll occasionally shoot and the lightning ball he shoots after being hit. Watch for the falling ceiling once he's hit five times.