Starting Items
Before you begin the Dragon Slayer quest chain, you'll need to gather several items. You will need one Hammer, one Lobster Pot, three Planks, one Silk, 90 Steel Nails, one Unfired Bowl and one Wizard's Mind Bomb. Because you will be fighting many monsters before you ever get to the dragon, it is also wise to have food or health potions, as well as good quality armor and weapons.
Magic Level and Gold Requirements
If your Magic Level is over 33, then you will need 2,000 coins for the quest as well. If you do not have a Magic Level of 33, you will need an additional 10,000 coins. Keep in mind that those coins are on top of whatever you need to spend in order to gather the other equipment that you will need. If you do not have enough money, you may need to do some simpler quests beforehand in order to get the coins you need.
The Crandor Map
Before you can head out to find the dragon, you will need to gather all three pieces of the Crandor Map. This challenge will be given to you after you accept the quest from the Guild Master. The pieces of the map can be collected from Melzar's Maze (near Rimmington), a chest within Ice Mountain and the prisoner Wormbrain within the Port Sarim Jail. Both Melzar's Maze and Ice Mountain will have hostile enemies.
Anti-Dragon Shield
The Anti-Dragon Shield is vital to your success in slaying the dragon. The dragon's fire-breathing ability can be devastating, but with the shield, your character will be able to withstand its effects. To get your shield, travel to Lumbridge Castle and speak to Duke Horatio. If you die during your encounter with the dragon, you will lose your shield. Because of this, some players choose to pick up several shields from him, just in case.