Remember to not upgrade your healing spell past 50%. When you fight the king, his attacks will remove 50% of your health, and heal only activates when your health percentage is less than or equal to (100%-HealthSpell%). If you have upgraded past that, remember to stock up on health potions, as they can be used whenever you've got some. I hope this helps.
To all of you getting a white screen, this is what I did to get rid of it.
I closed all other kongregate tabs, then I ate a biscuit, and then pressed refresh.