He there Fenngen, it's great that you are interested in such practices as meditation. The Vedas of India, written in Sanskrit, are the ideal source of such info.
Bhagavad Gita is a good entry level text.
Bhagavat Purana is another text of 18000 verses that mentions many yogis and their practices. You can find both at www.prabhupadabooks.com. I have studied them both fully.
Other texts on yoga and meditation include Yoga Sutras of Patanjali, which is very interesting.