An article with the basics of contemplative prayer:
https://www.contemplative.org/contemplative-practice/centering-prayer/
More detail from Thomas Keating (the father of centering prayer – 7 min. video):
https://www.youtube.com/watch?v=3IKpFHfNdnE
How to practice contemplative prayer (my own blog post, with lots of quotes and detail):
https://jasonnorth.me/spirituality/how-to-practice-the-highest-form-of-prayer/
Guides and courses from my friend Keith Kristich (his IG is also excellent):
https://keithkristich.com/
https://www.instagram.com/keith_kristich/