1. My oldest is now 22 and I am still teaching her to drive - the finer points take time.
2. I started in a parking lot as well but the point I missed was teaching them how to park while I was in there. That would have saved me 2 deductibles so far. Parking seems to be more difficult for them than driving.
3. Patience from you is key. They are nervous as hell and don't want to disappoint you or fail so yelling is almost always a bad idea.
4. 3-4 practices in a parking lot followed by some trips around your neighborhood are good before getting them on the road.
5. Once they are comfortable with the mechanics of driving, then, and only then, should you get them on the highway. When I did this I had them merge onto 66 and drive to the next exit and turnaround and merge the other direction. I repeated this for about 45 minutes ... but I did it at 8:00 am on a Sunday. I wanted them comfortable with merging onto the highway before I worried about dodging traffic at the same time.
6. Helps to have a full liquor cabinet at home as a post-game activity.

Prayers.