And only interrupt stuff that needs to be interrupted. For example, 360 AoEs prevent melee DPS and yourself from being in range, so interrupt it. A cone attack can easily be dodged and you wont be taking any damage while the enemy is charging it, so just let it happen.

I think enemies can also become immune to stun, so perhaps it's best to use is sparingly for that reason as well.

I know lancer has a non-GCD stun. Perhaps other classes have one as well. I feel like they're better suited for stunning due to that, but sometimes you can't rely on people.