Pratyahara (Sanskrit, rejection or withdrawal) is a technique for diverting the senses from external to internal. It is also the holding of the "here and now" as well as the name of the 5th limb of yoga according to Patanjali.
This pulling and diverting of emotions and feelings from outside objects, impressions, associations, emotional reactions, and sensory perceptions is the directing of consciousness inward to the depths of the subconscious. This is where the roots of all our human limitations live. Because of this, Pratyahara is the foundation for concentration (Dharana), meditation/contemplation (Dhyana), and enlightenment (Samadhi).
How does one withdraw from sensory perceptions? You probably already do it all the time. For example, someone who is occupied with work that requires significant visual attention may not feel the tactile irritation caused by a fly running across their face, since a greater focus has obscured the weaker one. Similarly, during yoga, if we direct our consciousness and attention outward, to objects outside ourselves—those on the mats next to us, the teacher, our surroundings—we may not notice the subtle processes, changes, and sensations happening within us. They would be overpowered by external impulses and annoyances.
In my yoga practice Pratyahara is achieved by three methods: The use of special pre-routine techniques such as "Tadasana Pratyahara", mentioned below; the cultivation of immobility in the physical body after entering the asana's final form; and the use of drishti (immobile gaze).
1. Tadasana Pratyahara is a technique for working with attention and breathing that I use in yoga practice before each session:
Stand in Tadasana. Spread your attention all over your body, so that you perceive the whole body volume simultaniously, instead of your attention being narrowed and focused on one particular body area (usually it's focused in the head, or in the aching body parts, or in any other area your attention goes at this moment for whatever reasons).
This technique allows one to switch consciousness from external objects to processes internal to the energy body, which prepares the consciousness for Practice.
2. Immobility of the body
Once the practitioner has fine-tuned the energy-geometric body position of an asana (which takes as long as is needed for the practitioner to really feel the position), the goal is to remain immobile within the pose to allow the energy to distribute throughout the body as needed. This immobility allows the lines of energy to arrange themselves in the correct energy-geometry to bring the most benefit to the body in the pose. Any chaotic movements while this is happening, such as side-to-side movements of the head or micro-movements in the arms and legs, disrupts this internal process and "smudges" (decreases) the effect of the asana.
3. Immobility of the gaze in yoga practice
A wandering gaze signals that one's attention is outside, not inside, and implies an inability to concentrate. When this happens, the deeper yoga is not occurring. By concentrating our gaze on an object or a specific point, we create a dominant focal point that suppresses all other focal points or centers of irritation. This gives us the chance to leave outside stimuli and go within.
Pratyahara is the bridge between external yoga techniques and the more subtle, inner practice of yoga.