Sailing on cargo ships is extremely instructive. You learn to take responsibility right from the start. There's a strong sense of hierarchy, but that doesn't mean you don't have a great deal of autonomy when it comes to your tasks. At sea, there's no garage, no fire brigade and no doctor: a crew has to make do with what's on board! Finally, I'd like to add that you have to enjoy working in a team and, beyond that, living in a community.
During embarquement, I mainly sailed as a deck or engine watch officer.