During my time in the training camp, I used to read a book on sight-singing during every personal maintenance period.
Eventually, I finished the entire book and revisited about half of it by the time I was discharged.
Indeed, there seems to be nothing better than sight-singing for improving one’s musical ear.
It became easier to recall perfect pitch, and the music I imagined in my head sounded clearer, making it easier to spontaneously come up with melodies. Also, when I hear a melody, it is easier to understand it in terms of solfege. In other words, it seems like my ear training skills have improved as well.
Let’s not neglect sight-singing practice.