Recommended Reading
Mindfulness with Breathing: A Manual for Serious Beginners
Ajahn Budhhadhasa Bhikkhu
Lays out the practice of anapasati meditation, literally mindfulness of the in and out breath.
"I do not perceive even one other thing, O monks, that when developed and cultivated entails such great happiness as the mind. The mind when developed and cultivated entails great happiness.”
~ The Buddha
AN 1:9