Sometimes the question just isn't the right type for the site. I read your question when it was first asked, when you asked why, and now again.
The problem I see is that you tried to train somebody before and you weren't happy with the experience. The only answer I can give you is: take what you learned last time, think about options to try, and try them. After you have been a mentor several times you will get better at it, or you won't.
You are expecting a long answer you even lay out the three parts:
The answer I would have expected would have been something like that:
There should be 3 axis of improvement for a Junior. 1 - The Technical
part 2 - The understanding of the (software) shipping flow 3 - Work
As for the first one, the Junior will be asked to follow the project
at hand with precise set of goals to achieve linked with some bonus
goals. (Ex. in software engineering, we are making web services so we
are expecting basic understanding of the messages flow, actual use of
the architecture, etc. Bonus goals would be: challenge of the
architecture, recognition of room for improvement part of the code,
and implementation of new architecture for a 'in scoped' project)
As for the development in the team, the understanding of the shipping
flow is very important (more over if the Junior does not see himself
as a long term developer). The understanding of the business, tests,
deployment, etc. All of these things have to be integrated full in the
first 4 months. Bonus point for pointing out problem in the flow and
ways to improve.
Finally, the work ethic. For a Junior to enter a new company will
define his behaviour for the rest of his carrer. It's important to
spot short coming in communication (verbal, writing etc.) and
encourage certain kind of behaviour (sending a mail to re confirm an
oral decision for instance). It's also interesting to develop his
curiosity toward all of those soft skills as it would greatly help him
Unfortunately for me your question as constructed makes it even harder to answer. You have no specifics in the question but want a long answer.
The best advice may be to ask the company for help; ask your boss for guidance (the boss can mentor you), or find a book.