How do I start implementing DMARC (p=none)?

First ensure your primary sending systems such as your ESP and corporate mail provider already authenticate with SPF and DKIM. This gives you a clean baseline.

Then publish a monitoring record:

v=DMARC1 p=none rua=mailto:crew@tidalmail.com

This collects reports without affecting mail flow. It is the scouting phase of DMARC deployment.