SPONTANEITY
off-the-cuff
spontaneous; without preparation or rehearsal. (Informal.)Her remarks were off-the-cuff, but very sensible.I'm not very good at making speeches off-the-cuff.
play something by ear
to improvise; to decide what to do after one is already involved in a situation.When we get into the meeting we'll have to play everything by ear.He never prepared his presentations. He always played things by ear.