Dave you need to start with a paper pattern, which will tell you how to go about making the panel.
Where you need to cut the paper to make it sit flat, is where it needs stretching and where the paper need folding, is where the panel needs shrinking.
On flatter areas where the paper sits fairly well, you can leave that area more or less alone.
Have a look at all of Peter's movies here
https://www.youtube.com/watch?v=cX-lO0mwqQo
Watch them and then watch them again. Have a practice in the workshop, when you are not sure, watch the movie again. Practice, practice, practice.
If you don't have a wheel, you can still make nice panels, it just takes longer,
Cheers Charlie