A) Ruck for 1 hour w/ 20% of bodyweight.
Nasal breathing only - let the demand for oxygen dictate your pace. Nasal breathing connects you to your diaphragm. Feel the air expanding your belly and lower ribs.
You should go as fast as you can without having to mouth breathe. Over time, your pace will increase.
Do not run while rucking!
Focus on good posture. 80% of the pack weight should be on your shoulders, 20% on your hips. Highly recommend a pack with a hip belt.