To play something by ear means to improvise.
To decide how to deal with a situation as it develops rather than acting according to plans made earlier.
To let things go as they may.
1. A: What are you gonna do this Friday?
B: I think I’ll play it by ear.
2. A: Where are you off to after the party?
B: I’m not sure, I’ll probably play it by ear.
3. We haven’t made a decision yet. Let’s just play it by ear.
4. A: Where should be meet later?
B: Can we see how things go and play it by ear?
improvise, make it up as one goes along, take a situation as it comes, think on one’s feet