What any actor could learn from Karen...
No matter what the role is, take it 100% seriously. After watching Guardians of the Galaxy for the first (and second and third) time since the theater, she stands out head-and-shoulders above any actor despite her limited screen time. It really feels like she had become this character: Nebula while a lot of other characters were a famous actor being called by another name. The only other character I'd give a close 2nd place was Bradley Cooper's Rocket voiceover.
I'm won over; I will watch anything with Karen Gillan now.