My total power is increasing so sloooowly...

I'm only halfway through chapter 2 of the story, but it's super fun, there's a ton to do, and I'm not getting bored at all!! However, my total power has started increasing really slowly, so how are you all getting stronger? I've only managed to break the level cap properly so far... and I'm only using gems once a day... should I be using them more aggressively? How are you all training your characters?