One thing that has worked for me in the past is to do some regularly scheduled pair programming. When I'm driving I narrate my thought process and encourage questions. They get to see things and when I make a little typo and they can catch it, not only does it save me a few seconds but it makes them feel GREAT that they helped the senior dev. Making this highly interactive and the senior driving FIRST makes it still "fun" when the junior is in the driver's seat.
One of the biggest skills you're helping a junior to learn is how to break apart a big task into small, workable components. Maybe they are assigned a user story, but that user story is going to need multiple functions written, or something like that. So you might start with pseudo-coding or creating the interfaces together, talk high level about how a particular method should work, and then let them do that part by themself. "Let me know if you get stuck or done with that and then let's do a little informal code review."
Beyond that it's the normal management stuff of compliment sandwich on negative feedback, etc. The normal things you do to build and maintain rapport with coworkers.
