Plant a lot of fruit.
Level up your life.
I just beat the third boss I believe. you have to knock four armoured talismans off of it with a few combos before you can do any real damage to it, so you have to save your magic up for THAT time, otherwise you won't really be able to hurt it...
Right after, I was fighting enemies who could do about 1/7th of my life to 1/4th with one power hit, and there were like five in close order.
You really have to watch the radar, use your magic, and be careful.
And I've only scratched the surface...