Basic Procedure
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Generally, we accept the defaults.
What comes with a clone?
All Data
Attachments do not come down in a clone unless the appropriate option is selected when requesting the clone.
Diff Utility
Whenever test is cloned, all the in-flight update sets must be reapplied in order. To help with that task, you may want to use this utility: https://github.com/wwest4/ServiceNow/blob/master/ServiceNow/diff-instance.py - it can give you the update sets and order, minus the sets that have already been applied to prod.