personally I logged a few thousand miles before I figured I was ready....basically make sure you're comfortable with the bike and yourself...get some time on the street, and make sure you teach her the proper riding techniques (hand placement<this one is crucial>, looking, not to act like a frog, etc...)
Arms around your body, hands on the tank...this causes the least amount of pain to you under breaking...when cruising along its cool if she sits up and just holds on, but once you get more agressive in your riding, its going to be much easier on you and her if she puts her hands on the tank in front of you.
In the beginning, look where your turning...no leaning, no leaning the opposite direction because she thinks the bike is gonna fall over, and remind her no hopping around while in a turn. As you both get more accomplished, she should begin to lean on her own naturally.
No hopping around
...just cause her ass isn't comfortable doesn't give her the right to turn your bike into a pogo stick.
More people will add their two cents, but this is a good start