General

@stevenman76: Stacking Panic, I assume, is the buff you get for 10 seconds when you hit an enemy with Panic. You can stack the buff up to a total of 10 levels and will increase the number of orbs used per consecutive Panic, and each level increase "reduces the amount of damage you take." No, it's not worth it since your damage suffers instability.

In what @silverfoxr said, use puncture before panic in the beginning. Panic gives you a debuff that makes skills use up more combo orbs, so you should use it after puncture. What do you mean by "stacking panic"? Using panic more than once before the time limit runs out only does two things:
-Increases the duration
-Makes all of your skills cost an extra combo orb
Also, it should be noted that Panic should only be used when youre not going to kill the boss in around 7(If I remember right?) hits. As for puncture, this depends on your crit rate. I believe the extremes of when to use puncture are at 15 hits to kill and 21 hits to kill, or at least somewhere around there(15=100% crit, 21=0% crit)

@silverfoxr: so should I not bother stacking panic and keeping it at 1? Does it even do anything by stacking? I can't see anywhere in the skill description that it does.

Build your orbs to max with RB, activate Enrage, hit with Panic and Puncture, continue to spam RB until Panic runs out, re-apply, repeat until Puncture runs out, re-apply, repeat process until boss dies.

EDIT: If you're fighting a stationary boss, you may also have to take a step forward once in a while to prevent the anti-botting system to kick in and stop your attacking. Also, obviously, keep all your buffs on whenever possible.