If we were to find ourselves in a weightless, gravity free environment balance practice would be meaningless. Balance of our bodies assumes a frame of reference within which we are blancing. I think for yoga this is one of the most interesting aspects of practicing balance. In yoga one of the first journeys we take is an inward journey.... learning to listen carefully to our bodies, to connect our bodies to our thoughts and our breath. But a journey only inward is inherently sterile. We do not exist in that contextless space, and balance is a way of moving out of ourselves and finding context to our world.
A posture, after all, is different depending on the orientation of our body within the earth's gravitational field. Stand on one leg and lift the other, knee straight and hold it at a 90 degree angle. Now lie on the ground with both legs straight and lift one leg up to a 90 degree angle and feel the difference. If I had a clip art of that pose I could reorient it within a picture of the room in lots of different angles, but the posture would change for the person doing it as the pull of gravity moves through different joints. This is a basic principle for anyone who lifts weights.
When I prepare to enter a standing balance position I use a particular seequence of cues designed to find inward stability, and to connect that outward.
First I go through basic cues for alignment: feet connected to the earth. A good cue here is to imagine you walked across a giant ink pad and are walking on rice paper. Imagine what your foot prints would look like, and if you need, for example to lift up into the inner thighs to pull up on the instep, or shift weight on the pelvis to balance the weight evenly start there. Check for center of gravity by rocking forward and back a bit, feel if the low back is tight, and put softness in the knees, or a tuck in the pelvis. Be aware of the natural curves of the back. (People with real problems with spinal alignment probably want to do some alignment work before starting balance... using a plumb line to help see where they need to shift, and doing some basic strengthing and stretching to help create better alignment).
Using mula bandha, udiyanna bandha, and jalandhara bandha are very helpful. They help create alignment, but also help keep it.... working synergistically with the pull of gravity. Basically imagine you are holding an apple between your chin and your breastbone, then that you are holding a dime in your navel, and that you are doing a kegel.
Anchoring oneself within space can be done with the drishti, or the line of sight. Choose an object on the horizon as your anchor. Something that is not moving (or not moving in relation to you. Recognize that the earth is moving, the universe is in motion.... but the earth is stable in relation to your body, and the other object is stable in relation to both you and the earth). I like to choose something that seems either beautiful, or meaningful to me, something that reminds me of the value and interconnectedness of our little corner of space and time. Imagine this as a weight, and your gaze as a thread and mulha banda as another weight. The gaze balances between the inner and the outer, drawing us both deeper into and further out of the maze.
Use not just the outer senses of sight, and sound, but also the inner kinesthetic cues. If balance is challanging for any reason have a chair or wall near you, or start with your hand actually on it. Like a child taking a first step holding a parent's hand, that wall or chair will help you learn to find and use those inner cues.
Remember to breathe. People have a tendency to hold breath while balancing. It is as though the idea is that to balance is to be completely still. Remember though that we are never totally still. Journey inward and the heart is beating, cells dividing, electrons spinning. Imagine yourself on a surfboard, or just riding up and down on the waves, or riding dressage... all balance is flow.. is riding the waves... is maintaining control.... not fighting the wave, or horse, or just the space your body inhabits, but connecting to it in a way that honors and understands body, mind, breath, and the space through which they move.