General information 

big brows make it look aggressive 

ears usually look like fish fins 

add shadows under the eyes, for a dark look 

little scales to add details

neck scales are a lote bigger

more volume with extra scales

1- long neck and snake/crocodile type of head will make vicious and nasty 

2- spikes everywhere 

3 and 4- for a bulky dragon, short nose and a rhinoceros kind of look, short horns, short spikes

wings

There are already many tutorials for dragon wings. The basic look a bit like bat wings. For original wings, you can add feathers 

add shadows for scales to create a volume effect

add small scales to increase the level of details 

neck scales are big and more impressive 

scales

It depends on the type of dragon, water dragons won't have the same scales as earth dragons. No need to put scales everywhere, you can add them as a detail here and there 

dragon tails

Depending on the drago type! it can be basic or have a more complicated shape