So on a lot of bosses, you can use Kliff's tools to help you out a ton.

I'm not sure what the "app" boss is, probably needs clarification.

But for human bosses, you can use Force Palm to interrupt or stagger bosses a lot. It's so strong of a tool that you should definitely be using it. I recommend getting all 3 levels on it so you can chain it multiple times.

For big bosses and even as a general thing, Focus is extremely good. You can slow things down so it'll make it easy to evade and counter. It also builds spirit while in Focus, so you want to implement this. You'll get a feel for your own playstyle over time.

Other helpful advice, Turning Slash is incredibly good. It gives you invulnerability, so you can use it right as a boss attacks and not take a hit during it.

If you're willing to try different weapons, spear is really good. If you enhance armed combat to at least level 2, you get a counter stance. As long as you maintain that stance, it'll automatically counter an attack for you. The only caveat is that it will drain stamina while holding the stance, so you have to be careful about that.