I totally echo everything said so far. A good ASM is worth their weight in gold. Be wary of the barefoot with the miniwelders, and also of the ones whose first reponse is "that can't be done." Praise and encouragement is essential, but also be very clear and firm at the very beginning as to what you expect, and that you are there to help them. Hold them to your standards, don't let them get away with blaming things on other people- especially on actors. ASMs need to know that they are responsible for eveything, just like you are, and even if something happened because of someone else, they should be actively taking steps to make sure it doesn't happen again.
There are a few essentials I do give to my new ASMs, though which you might consider: I give them a black fanny pack with band-aids, safety pins, and a supply of glow tape already cut into little 1" pieces. I tell them I expect this to always be on them in rehearsal and performance, they need to refill it as necessary,and that they need to get themseves a small maglite or LED blue flashight as well. At tech, I bequeath to them, "The white gaff, that makes all things visible to actors; and the black gaff, that fixes all things. Keep these in your reach at all times, and the show shall run smoothly."