Shell that only you can run is not automation. The next person has to read the script, and in six months you are that person. The bar is the same as for any code: state what it does, refuse to do anything surprising, and make each step checkable.
About 2 min of reading
Write a dry run guard.
The guard
Before you run it, say out loud what it will print. Then open the answer.
The habit it encodes
Before you run it, say out loud what it will print. Then open the answer.
A file called build.sh that builds one thing is reviewable on its own. A giant script with twelve modes has state that only makes sense in the middle, and that is the kind of script nobody can hand over.
Clean up temporary folders on exit, including on failure. A script that leaves debris behind fails the next run, and a failure that is caused by leftover state is the kind that makes automation untrustworthy.
A comment block naming the inputs, the outputs, and the side effects. A reader then knows before running whether the script writes files, and there is no surprise in the middle of a run.
Print the commands instead of running them unless a flag is passed. A script that shows its plan by default can be reviewed by anyone, and the destructive mode is a deliberate choice.
When a step fails, print which step and what it was given. A script that exits with a number tells you nothing; one that names the step and the input tells you where to look.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.