A couple of things that I do when I have interns:
Assess/observe the person. As a mentor you need to understand what his/her weaknesses are and what the their strengths are. For example they might be really good at analysing problems but have confidence issues, and might be afraid to ask questions, you need to uncover all this to be productive with them.
Ask the person what do they want to be and what do they want to learn. Asking is usually the easiest way and you as a mentor knowing your company will then be able to accommodate based on the intern's response. Also ask about their hobbies and side projects, this will allow you to better maximise their potential.
Expose them to different areas and workings of the company (engineering, devops, testing, analysts, sales, etc)
Be honest and humble. No one knows it all.
Good luck!
How to Manage-Up... that is to say, how does one anticipate a superiors needs/solve problems/present information, especially with difficult, demanding, intimidating bosses.
If your intern can master this-- it will be a huge career advantage.
Have one on one meetings and learn how else can you support him/her
If you passed that stage, I recommend the book The Pragmatic Programmer as a very good book on how to become a good software developer. The book Clean Code is a good starting point too.
Other than it depends on your circumstances. A good heuristic (particularly in frontend world) is to study the language, not frameworks.