There are only 3 Dragons currently in Guild Wars 2 each of them spawn once every 3 hours from their previous death. For example if a dragon is killed at 1pm they will spawn again at 4pm. There have been times where the dragons spawn ahead of schedule maybe we influence it or maybe it's just the developer's having fun, we don't really know yet. The three dragon's spawn locations are in Sparkfly Glen, Frostgorge Sound and Blazeridge Steppes.
If you don't want to view this page as one long page here are independant guides for each of the dragons
Zone: Blazeridge Steppes (40 - 50)
Closest Waypoint: Lowland Burns Waypoint (Nothern end of zone)
This is the lowest level and one of the easiest dragons there is. The dragon is mostly a straight forward fight once he lands, just deal damage to him and at about 50% he will summon an army of adds for you to kill. Take out all of his adds and continue to focus on the dragon. He'll be down in no time and you'll get your chest of loot!
Oddly enough the prequest can be harder than this dragon depending on how many people you have waiting to do it. For the prequest you'll need to port to the waypoint just to the south of Lowland Burns Waypoint, the Guardian Stone Waypoint. From here you will want to head just to the northeast to the Shattered Palisades. Here you will need to collect Siege Weapons for Crusader Blackhorn which will be used in the fight against The Shatterer when he lands. Hence, pre event! (or quest if you prefer that).
Now the reason this could be harder than the actual dragon event is because depending on how many people you have you'll have to collect more and more Siege Weapons which drop from the Ascalaon Ghosts. This could take ages especially since the ghost's camp is so small. However once you get that done you can just run right on up to the dragon and take him out!
Zone: Sparkfly Glen (55 - 65)
Closest Waypoint: Splintered Coast Waypoint
This is another extremely easy dragon to do. All you have to do is pretty much damage the dragon once he lands. Ranged and Melee are both able to attack him although he has a giant AoE fear and drops poison clouds both Ranged and Melee will have to move out of. At certain points during the fight Tequatl will also summon big fat guys that stomp around and attack everyone fighting him. It's important you take out these mobs as well as any other adds that come and attack you during this fight. If you don't you can quickly get overwhelmed and that is definitely no fun.
Also throughout the fight you will see a notice for the Asura Lazer charging up to fire at the dragon. Defend this lazer from the local risen that come out, when it fires it does a great deal of damage to the dragon.
Zone: Frostgorge Sound (70 - 80)
Closest Waypoint: Earthshake Waypoint
This is the hardest dragon, as you could have guessed since it is the only one in a level 70 - 80 zone. As with all previous dragons the fight's tactics are shown below your minimap where it displays current events. However if you want a quick run down of the entire fight here is a step by step guide.
1. Take down all of the Dragon Crystals
2. Fight off the Ice Golems that land and attack the cannons
3. Destroy the Corrupted Ice Shield
4. Damage the Claw of Jormag to deal damage to the dragon
5. Fight off the Ice Golems that land and attack the cannons (again)
6. Destroy the Corrupted Ice Shield (again)
7. Damage the Claw of Jormag to deal damage to the dragon
8. Once the Claw of Jormag reaches 25% it will take off and land in a new location starting the final phase.
9. In the final phase here the most important part is destroying the Ice Pillars to protect your golems to getting to the Claw of Jormag. The bombs they carry are vital in stunning the dragon which allows you to deal damage to him.
10. Be sure to focus on the ICE PILLARS and not the dragon or the Champion Icebrood Wolf or Champion Icebrood Golem