Where Do I Begin?

The best way to move through the process of preparing a ceremony is to collaborate.  This is the time to reach out for help and to accept it. Don't be afraid to ask for support.
Involve those who were dear to the departed to participate in the ceremony.  Don't overwhelm yourself and let the process become stressful.  Check in with how you are feeling and do only what feels good to you.
A trusted Celebrant is also able to put together an entire ceremony with minimal direction, if needed.