Yoga and t'ai chi are usually begun as exercises - movement therapies - that strengthen and stretch the outer body, while developing sensitivity and awareness of the internal body. This increased internal awareness guides one inward toward the spinal cord and brain - ultimately to that mysterious place from which we came - a felt sense spiritual practice. But you can also practice them if you just want to feel better!
For posture instruction, group classes are a great way to start. Eventually one develops a personal, (mostly) daily practice, checking in with an instructor regularly. For meditation techniques, I recommend the teachings of the Self-Realization Fellowship, whose lessons can be learned through correspondence.
