1) Analytical approach from the Yoga Sutras (https://en.wikipedia.org/wiki/Yoga_Sutras_of_Patanjali) - Pratyahara (withdrawal of the mind from the senses), Dharana (concentration/focus), Dhyana (meditation), Samadhi (absorption). The key is the last three which are practiced together on some chosen object and is named Samyama.

2) Experiential approach through any activity (eg. Bhakti/Tantra/Hatha etc.) also called Laya Yoga (i.e. yoga of dissolution) where one "dissolves" one's identity (i.e. no experiencer nor object of experience) so only the pure experience remains. See the sections on Laya at https://en.wikipedia.org/wiki/Yoga , https://en.wikipedia.org/wiki/Kundalini_yoga and https://en.wikipedia.org/wiki/Hatha_yoga

3) Book of Techniques; Vijñāna Bhairava Tantra - https://en.wikipedia.org/wiki/Vij%C3%B1%C4%81na_Bhairava_Tan...

4) For a simple method to get started and more details, see my comment chain here - https://news.ycombinator.com/item?id=41537499