Inventory what the domain already serves
Before changing nameservers, list the records used by the website, email, verification checks, and any subdomains. Pay particular attention to mail exchange records and the text records that authorize senders or prove ownership. A domain can support several services at once, so checking only the homepage is not enough.
If you use a service whose DNS values are managed elsewhere, collect its exact record name, type, and target from that service. Do not guess missing values from an IP address you happen to see; a visible address may belong to a proxy rather than the origin service.
Switch only after the new zone is ready
Create the required records in the destination zone and compare them with your inventory before changing delegation. Keep a copy of the old zone values so you can investigate discrepancies. If an important record is unclear, resolve that first rather than treating the nameserver switch as a way to discover what is missing.
After the change, check the website and mail separately and confirm the records from public DNS lookups. If something stops working, identify the missing or mismatched record before making another broad change. This careful sequence helps preserve the services that depend on the domain.