Starting well.
WHAT TO COLLECT
Their contact details, including a phone number Their domain and where it is registered What they are moving from, if anything Who else needs access
WHAT TO PROVIDE
Account details How to access cPanel How to reach support, and when What is included Links to relevant documentation
WHAT TO EXPLAIN
That the domain should be in their own name That they should keep their own backups What they are responsible for
THAT LAST ONE
Establish early that updates and site maintenance are theirs, unless you provide it.
WHAT TO SET UP
Their account Their domain Email accounts, if required AutoSSL
WHAT TO CHECK BEFORE HANDING OVER
The site loads Email works Certificates are valid
WHAT TO SEND
A welcome message with everything in one place.
WHAT TO DIARISE
A check-in after a week.
WHAT THAT PREVENTS
Silent problems in the first days.