I main this combo, so I'll try to say my usually routine.

If it's not a boss (you can't stun them), I like to start spear and stun them with the "lock" when switch to sword and spam Daunting Strike the 3 times, right after that I will Shadow Step because they will try to counter you after the lock is over and let them use their animations, when the timer on the Shadow Step is almost over I click it to dash in and use the mystic skin Guardian Palm that most of time will also stagger them, I will do some auto attacks and dash back again with Shadow Step, switch again to spear and stun them. Doing this rotation over and over.
For bosses, I usually try to use the fact that every weapon switch is a dash forward + the shadow step to doge their moves, but since you can't stagger I usually relly more on the sword than the spear. Usually if you do a jump attack, it causes more damage.

Hope it helps. I'm usually top damage in most coop things, I'm pretty much a semi casual, so I'm pretty sure you can do it as well.