As soon as the cutscene is over, create a Hard save. check your inventory to make sure your Dragon is wearing all offensive stuff and all the skill points are spent. Now make a Quick save. Watch the series of arrows eminating from the Zepp. They indicate the path it is taking. Stay on that path and keep clearing ahead of the Zepp. Don't stray off too far from that path. If you do, the Zepp catches up and gets itself in trouble. Q-save when you feel the Zepp is secure with lots of health, so that you don't have to go all the way to the beginning if Murphy's law strikes at you.
Also, don't let your Fire Ball go idle. That's your dmg dealer. Always hit with #1 key first and then finish off with your Breath (mouse Left button) while the Fire Ball is cooling down. As soon as it's charged, hit something with it and follow up with Breath.
Go after the Nests and the lightning towers. Don't concentrate on the ballistas.
After the midway point, you'll be able to tell the Zepp what to fire at; select lightning towers for them while you take out the entire island with your super bomb.
Good luck

ing for you!