Apprendre les ficelles du métier is a common suggestion to translate to teach the ropes. The similarity between these metaphors likely helps. Both expressions refer to the demonstration of actual practice and not theoretical teaching.
There might be a slight nuance between them though.
To teach someone the ropes was originally telling an apprentice sailor which ropes was to be used to properly operate a sailboat.
On the other hand, the ficelles rather refer to tricks used to ease/simplify a job, like the hidden (invisible) strings a magician uses to hold something up in the air.
Unlike the cordages, knowing how to use these "strings" can be but is not necessarily a best practice. That depends on what ficelles are being taught...
Ficelles can also be found in these expressions:
Tirer sur les ficelles: remotely handle things/people like a puppeteer.
La ficelle était trop grosse: the trick was too visible so it was discovered.
Se débrouiller avec des bouts de ficelle: getting by without sufficient means.
Trop tirer sur la ficelle: Ask for too much.