You can start by doing a full filesystem and database and put the same thing running on your staging environment under a different domain. Don’t do configuration under this installation or if you do bare in mind that changes will be lost since you want to periodically sync the production database with the staging one to make sure the environment remains similar. Ideally it should be as close as possible to your production one.
Don’t forget to deactivate auto-updates on production in order to test everything before going live.