In through the nose, out through the mouth. Expand your diaphragm on exhales, meaning your belly should extend, and compress it on inhales, meaning your belly should contract. Deep, long breaths, with each one, return your focus to your form. When you drift, and find your breathing is automatic again, and your mind has wandered, acknowledge the thought, and return your awareness to your breathing. In through then nose, belly contracting and chest expanding, hold, out through the mouth, belly expanding and chest contracting.

All that to say, manual breathing is something I think everyone should practice regularly.