To use a hunter, you need to repeatedly tap on a tower to deal damage.

Warriors use FlameThrower attack. To deal damage, hold over towers. The best way to fly is to focus on destroying one tower 100% before moving on to the next one.

For sorcerers, you must swipe over towers to deal damage. These dragons rely heavily on their rage/spells.

Invokers are harder to fly and less common than Hunters, Warriors, or Sorcerers.

Their attack is different from a Hunter, but almost the same.

You are given four 'fireballs'. The first three act as general attacks, but the last one is like an AOE spell. It will take awhile to recharge the flames after you cast the last fireball.