1
general::
Phrase(s): wing it
to improvise; to do something extemporaneously. • I lost my lecture notes, so I had to wing it. • Don’t worry. Just go out there and wing it.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Improvise, as in The interviewer had not read the author's book; he was just winging it. This expression comes from the theater, where it alludes to an actor studying his part in the wings (the areas to either side of the stage) because he has been suddenly called on to replace another. First recorded in 1885, it eventually was extended to other kinds of improvisation based on unpreparedness.
American Heritage Idioms