Proprioception is your sense of where your body is in space, built from receptors in muscles, tendons, joints, and skin. It lets you control movement without watching yourself, and it improves with balance and single-leg training.
These signals combine with the vestibular system in the inner ear and with vision to give a continuously updated picture of where your limbs are.
It allows you to touch your nose with your eyes closed, to place a foot accurately on uneven ground, and to adjust mid-air before landing. In sport it underpins balance, landing control, and the rapid corrections that prevent an awkward step from becoming an injury.
Joint injury damages some of these receptors and disrupts the signals from others. After an ankle sprain, for example, proprioception at that joint is measurably reduced, which is one reason repeat sprains are so common. Rehabilitation that includes balance and control work, not just strength, is important for this reason.
Progressively reduce the information available and increase the challenge. Start with a single-leg balance hold, then close your eyes to remove vision, then add movement with a Y-balance reach, then add unpredictability with perturbations. Single-leg strength work such as split squats and single-leg Romanian deadlifts contributes as well.
Barefoot work on varied surfaces, where it is safe, increases the input from the foot. Small doses are enough; this is a skill that responds to frequency rather than to long sessions. The wider neural context is covered in The Nervous System and Athletic Performance.