I've also seen a number of tutorial on doing this and I think one of the big things is having someone else to help you, if that is not an option, then I'm afraid you may not get the template perfect.
From what I have seen, getting a nice smooth and tight layer of cling film around the area you want to template first is the key, then getting someone to carefully wrap the duct tape slowly in a single direction with only a small overlap between the layers
will give you best results.
Like I say, not done this yet myself,. But that seems to be the way I have seen it done most with best results.
What I will add though is the pieces never look perfect even when people have done it loads, I guess that is why you transfer the pattern over to cardstock when done.
Look forward to seeing your results.
Kind Regards, Myles Pope. Sent from my phone, please forgive any spelling mistakes.