There are many folks who have commented, discussed and taught grips. I have spouted my 2 cents: use the power grips.
But there is very little understanding of how to hold the disc, relative to the ground or the thrower's body.
In a forehand stance (i.e. facing towards your likely targets, usually with a forehand mark on), you could hold it a number of ways.
In a wide, blade stance like Dan (or Jeff). The disc face is roughly vertical.
Or in a wide, flat stance like Liz. This disc face is horizontal.
Or in front of your body, with two hands like Kristy.
Generally, I think the wide, blade stance is best (the first photo). It is ready to throw in an instant. It is easy to hold with one hand since the thumb and webbing support most of the weight (a horizontal disc needs to be held level by fingers working sideways - this flops around for many players). And it encourages throwing with a short, quick snap of the wrist rather than a big body and arm wind-up, which is preferable for any pass under 20 metres.
For a backhand, the grip is stronger, so the "flop" is less of an issue. Holding it wide is still key, whether it is one hand or two hands.
Let's get the new players ready to throw the first time they are taught ultimate.