The purpose behind meditation is to turn off the internal dialogue, that part of the thinking mind which is constantly chattering, and allow the instinctual mind to take over.
The thinking mind is important to us. Without it, we could not reason and shape our creativity. However, the thinking mind is often overwhelmed by emotional states, trying to categorize them and deal with them through logical and rational method. The instinctive mind knows immediately how to deal with with emotions. Also, in Taijiquan and Yoga, the body will learn the correct positioning and flow of the individual postures. Often the thinking mind will second guess what the body has learned. This can be harmful in deep Yoga positions, and even more harmful in a combat situation where you're attempting to use the Taiji form immediately. The instinctual mind knows to get out of the body's way and let it do what it has been trained to do.
Meditation is practiced from a comfortable seated position. Sitting on a chair or bench is permittable when leg and hip flexor flexibility is an issue. However, the practitioner should avoid reclining against the back of the chair and instead sit up straight, supporting their own back if possible. Traditionally, meditation is performed sitting on the floor or on a cushioned bolster.
During meditation, the practitioner should relax their body as much as possible, and avoid any strain and distractions. The breath should flow slow and deep through the nose, and the tip of the tongue should touch the roof of the mouth.
This is the first meditation taught in the Zen Buddhist tradition, and can be very powerful in training the thinking mind to turn off the internal dialogue. A game is played with the mind where the practitioner counts their inhales and exhales (i.e., inhale "one", exhale "two", inhale "three", exhale "four", and so on...). Between breaths the mind must remain silent. If the practitioner catches the mind talking, they start their counting over again at "one".
Once the practitioner becomes adept enough at this exercise that they can reach 9 or 10 without internal dialogue, they should lengthen the space between the counts by counting ONLY the inhales.
For some, the counting portion of counting the breaths can be distracting to turning off the dialogue, and prefer a more visual meditation. Following the Breath meditation is done by following the breath with your imagination as it flows in through the nose, down into the lungs, and back out.
After the practitioner has warmed up by following the breath, they are encouraged to focus their imagination on the tip of the nose, called the swinging door where the big chi of the universe mingles with the little chi in their bodies.
With this meditation, as you inhale say in your mind: "I am relaxing my body." As you exhale, say: "I am smiling from my heart," and smile. Keep your breathing long and deep enough that there will still be space between those phrases to allow the mind to quiet.
If the phrases are too long, you can modify to simply say: "I relax" and "I smile." After a while, you won't have to think anything, you'll just relax and smile without thinking.
Often in Yoga, the blocking of the four senses; smell, taste, hearing, and seeing, are physically blocked. For this meditation, the discipline of the mind is used to block those senses as you mentally focus on the point between your eyes.
This is the simplest and most difficult form of Zen meditation. The first thing the mind will want to do is focus on a single sound and explore it. However, this can often get the dialogue chattering away. The goal is to listen to all sounds without lingering on them; expanding the range of your senses ever outward.