Singers must practice technique for the whole of their career! I know it sounds obvious, but many don't. They reach a point where they think a quick warm-up in the dressing room before the show starts is enough. It's hard to imagine a violinist, guitarist, pianist, trumpet player, etc, not doing regular technical work on their instrument. Obviously we singers can't do the hours of practice that instrumentalists do because our instrument would fatigue, but an hour or two a day, five days per week, of technical work is the minimum. Be sensible and don't practice if you have a cold or are tired from a performance the evening before, but otherwise it has to be your daily priority. By practicing technique I mean concentrating on technical passages that are challenging and difficult, not just warming up the voice on easy scales.
Examples are improving coloratura, register transition, piano singing, extremes of range, vibrato control, dynamic control, diction, language pronunciation and so forth.