What generates enmity?

[Viviza]

It'll happen from time to time that you'll be doing something just as the tank pulls. It happens. Just don't keep a regen up.

You can fuss about with cards, heals, and buffs, on targets not engaged in combat, and none of the monsters will notice. It's only when you initiate a pull or interact with someone already in combat that monsters will register your actions (edit: exception -- bosses automatically put everyone in combat). So you can usually draw cards safely provided you haven't healed anyone yet.

Random aside: if you're low on MP, you can just idle outside of combat for a bit. You regen MP much faster out of combat, and aren't technically in combat until you get yourself involved. It may look like you're being lazy, but it's effective!