It's been an interesting and successful experience thus far.
* A training schedule, similar to a degree plan in university - just something that outlines where the organization expects them to be at 3, 6, 9 and 12 months during their first year of employ.
* Coding standards defined by the organization. Telling any developer, but particularly a junior, that your standards are "I know it when I see it" doesn't fly.
* Formal code reviews. This is something we could definitely do better. I'm working getting Atlassian Bamboo to make the reviews easier on everyone involved.
* Regularly scheduled meetings with the trainers and the junior. We do every 3 months, with less formal meetings more frequently. It's important to let them know how they are progressing, and to give them tips on how to improve any deficient skill sets.
Overall, I think the most important thing is to maintain open lines of communication.
Mapquest does not currently have anything like that, and I'm not sure we're set up well for that sort of thing at the moment (I'm not sure what they'd do). We have interns in our marketing department and I think the new, very young looking dude in finance is an intern, but nothing in development.