I'm still young compared to most here (27), and have had the chance to be in both roles. It seems like there are generally two types of "learners"

1. Agressive and enthusiastic, but inexperienced. Works fast, makes lots of mistakes, doesn't want to wait around for "explanations", but really wants to get the job done.

2. Enthusiastic but tentative and unsure. Never wants to proceed without advice, welcomes the more experienced hand to take over after encountering the smallest issue. Gives up easily.

I've found that with #1, the best thing I can do is shut up, wait in the wings and watch very carefully to be sure I'm right there to help when the inevitable failure, break, or accident happens. The key is to allow all failures to happen, short of those that would put someone in serious danger. This type of learner absorbs the most information right after something doesn't work.

With #2 it's more a role of helper. Whenever questions are asked, I make sure to turn things squarely back on them. Instead of "I think you should use a soft mallet at 12, 9, 6 and 3'oclock to dislodge that rotor," it will be something like "Looks like the rotor is stuck. What do you think we could use to dislodge it safely? Where does it seem to be sticking?" The idea is to keep from "taking over" the work and just helping to push them forward with questions only. Get tools for them, keep the shop clean, and show that they are in charge, but you're there to help.