When looking at the CT, look for 50% web reduction between primary rays and 25% between secondary, evenly spaced rays. All one kind of ray(single, double, or crossed, i believe double is favored for showing) halfmoon(180 degree) tail spred.
On HMPK decide if you want asymmetrical or symmetrical.
whichever one you have as dragonscale(probably easier to find a dragon HMPK) look for full even scale coverage, make sure it doesn't go into the eyes(can cause blindness).
body wise try to avoid spoon head, warped scales.
the wider dorsal is more favorable by a lot of breeders.
Color wise. I'd go with a black dragon HMPK male and a black orchid, superblack or similar CT female.
But, really, get whichever gender is the best for that tail type. (if you see a perfect CT male for instance, get that instead).
You can breed the dragon scale parent to a child, or breed the two best siblings form/fin wise. They'll carry the DS trait so it should continue to show up in F2, hopefully even better.