try not to: just your face should face forwards, your body mostly stays pretty much parallel with the direction you're going, and it's you're legs that are used to turn the board. At least that's how I experience it, and as far as I know twisting your upper body doesn't have much use, if any at all, in snowboarding?
Actually, you can be using your upper body as well. You're right in that when riding in a neutral stance you want to be facing parallel, but in your actual turns you want to be using both your upper and lower body as you get more experienced (depending on the type of turn you're using at the time).
The problem is 'dynamic riding' refers to A LOT of snowboarding. Some dynamic turning techniques involve having your upper body quiet while your feet are doing the turning, but many other turns require your upper body to aid the lower body to help execute that turn faster and with more power.
I *think* what the OP is trying to do is learn to turn using both upper and lower body to get more power and quickness in his turns and in this case he wants to be using both upper and lower body.
You want to be turning like this (either top to bottom or bottom to top... either works):
1) Head looks where you want to go
2) Shoulders and upper body follow head
3) Hips follow shoulders/upper body
4) Knees and ankles and feet follow hips
Basically you should be doing this with non-dynamic turns already, but the key to making your turns more dynamic is to not be passive about it. Don't just turn your head, body, knees etc and wait for the board to follow, if it's not turning fast enough, then power through with your whole body and FORCE that board to turn faster.
Push your shoulders, hips, knees, feet etc into the turn and drive that board with power. That's the difference between a dynamic rider and a beginner rider.
A strong, dynamic snowboarder will use his whole body to power through the turn and a non dynamic rider will go through the motions, but instead of pushing his snowboard to turn, he'll just sit there and wait for it to turn.