Look for repetition
Good candidates repeat frequently, use structured inputs and have a clear result. Moving an order between systems is easier to define than making an ambiguous business decision.
Keep exceptions visible
Decide what the automation should do when information is missing or a service fails. Give a person a useful explanation and a way to continue.
Measure the whole workflow
Compare the time spent running, checking and maintaining the automation with the work it replaces. Start with one bounded process before expanding.