The two invisible skills that separate okay improv from electric improv are presence and commitment. Neither is a technique you perform - they're states you inhabit.
Presence begins with active listening, but extends beyond it. It's not just receiving your partner - it's being fully in the imagined space, feeling the reality of the scene in your body. When you're present, you don't need to think of "what to do next" because the scene tells you.
Commitment is what presence looks like from the outside. When you're truly present, you don't hedge. You don't play your character in air quotes. You make a choice and you mean it - with your whole body, voice, and attention.
The connection between them: presence is the internal state, commitment is the external expression. You can't fake commitment without presence, and presence without commitment stays invisible to the audience.
Both are practices, not talents. You build them through repetition, through noticing when you've drifted out of the scene, and through the courage to come back fully each time.