play it by ear

Từ điển Oxford Advanced Learner 8th

play it by ˈear idiom
(informal)to decide how to deal with a situation as it develops rather than by having a plan to follow
•I'm not sure how many people are expected— we'll just have to play it by ear.
•I don't know what they'll want when they arrive— we'll have to play it by ear.
Main entry: ↑ear_idiom