Well, singers learn pretty quickly that there are no magic buttons to press to produce that perfectly in-tune pitch or wonderfully rounded tone. Unlike an instrument such as the piano, singers can't just produce the right note by plunking a key. They must listen intently and use their whole bodies to create beautiful singing. That's where the interesting cues from the conductors come in. A skyhook refers to how singers must use good posture (open their bodies for resonance) and hold their heads up (from the back of the crown) so that the throat is open for good tone flow. Fish Lips refer to positioning the lips around the vowel mold so that the tone is focused toward the mask of the face and not spread out the sides of the mouth. Getting the tone onto the upper shelf also refers to focusing the resonance of the tone forward to the mask of the face, rolling the feeling of vibration UP across the roof of the mouth to the backs of the upper front teeth, and then using a narrow vibrato to unify the sound.
Try as we might to be consistent, we humans can easily loose focus, or at least shift it somewhere else from time to time. Unfortunately, we need a lot of reminders to get us back on track. In the Mormon Tabernacle Choir, we are challenged to give our 100% effort every time we are in the loft. Even when we are reading the notes and words for the very first time, we generally have an audience and are expected to deliver a good performance. Our rehearsals are for polishing a performance -- definitely not for woodshedding parts (plunking out the notes). So, sometimes we as humans are focusing more on the lyrics than the notes or vice versa and need reminders now and then of where the "traps" are. We are encouraged to write in our music whatever we need to remind ourselves to use better breathing here, or to unify the sound better there, or to "get some lip around" those vowels, particularly on the high notes. Hopefully, the next time we come to those cues, we will fix the problems and polish the performance even better. We do not have the luxury of many weeks of rehearsal on a few pieces, like college or other community choirs. We have to become proficient in just a couple of sessions.
It's all about making the performance as polished and beautiful as possible. What can I say, conductors do what they need to do and say what they need to say to make it all work. So, as a singer, I hereby pledge to hang onto that skyhook, use my fish lips and get up onto my upper shelf -- 100%!