Some details I consider important:
The grey should be lighter, ideally a matte sliver
The scales do not need to be obvious or prominent (A smooth cetacean or shark-like look similar to http://www.furaffinity.net/view/23615620/ is good.)
The ears are bigger than the horns
The size is fairly arbitrary, and depends on a mix of mood and scenario
The male and female versions appear largely the same. On closer examination, the male's horns and mane are larger and he is overall slightly bulkier

Have been wanting one of these for ages and managed to grab a slot from   Fefairy

Char © Zephyr42

Art © fefairy