Keep moving; as long as you are flying at an angle to the ballista, they will very rarely hit you. Use Fire Sphere from a distance and you should be able to take care of the flying opponents and whittle down the ballistas, so it will be safer taking out the 3 nests (either with more Fire Spheres or getting close and using Fire Breath). Once you take out the nests you will automatically return to the battle tower.
Check your inventory; most dragon equipment gives skill bonuses. After this fight, you'll get access to a chest in the battle tower that you can use, which contains dragon equipment with very useful (non-skill) bonuses.
If you explored the start of the fjords you may have a dragon skill book you can use to learn Dragon Spirit, and can fly away behind the battle tower and use it to heal or otherwise rest up. If not, you will soon have easy access to alchemy material, so you don't need to conserve food or potions.
A burst of speed is triggered by right clicking or hitting the 'E' key.
first time dragon help needed pleaseWhy is dragon so hard?