Soft belly. Through work by myself, with my teacher, and my students, I have found that really committing to having soft abdominals will force a singer to find deeper and more profound support. To find this lie on the ground on your back. Let gravity allow the floating ribs to open like a clam shell. Let the belly be full but soft, like a water mattress.
This has worked some wonders. The results ought to be an easier navigation through registers.
Soft Face. Having a tight face means having a tight sound. There seem to be some deeper reflexes associated with tight faces, because when a singer lets go of the face, the sound usually gets warmer and easier. So I have found that by reminding students that vowels are primarily formed by the tongue then they usually can move towards relaxing the jaw and lips. If that does not work, then I will have them bend over and allow their faces to relax to such a point that gravity begins to pull down on them. They will then return to normal posture and sing with the same feeling.
Balance. I have some knee problems, and I believe they are due partially to an incomplete sense of how to stand. After doing some research, an easy way to think about balance is to imagine that each foot is a rectangle and has four corners apiece. The weight should be distributed evenly on each corner. If one is holding more weight than the others, then adjustements can be made. I find that this is a more positive way to go about having a centered stance rather than exclaming, “Stand still!”. The singer’s sound usually becomes more stable after doing this exercise.