Hah! Well, since you asked... get ready for a ramble!
Honestly, so much of drawing creatures and beasties is all about studying real world animals, which just means drawing from reference. I actually enjoy just eyeballing from photos- it's kind of meditative and relaxing. I've filled a lot of sketchbooks over the years by doing this... birds especially, because they are just my favorite. But find multiple angles, various expressions, etc. This will teach you the actual underlying anatomical structure, as opposed to just shorthand symbols for 'eye', 'tooth', 'jaw'.
Secondly, pay attention to flow! So much of the power of impressive creatures is in the posing of their body, coiling or unleashing power. Here I've curved the neck- But there are still contours which follow the curve, so that you don't lose the turn of the neck in space. It's not just a noodle-y hose, you've still got lines of tension to hold things in place.
Lastly (at least so far as I can think of off the top of my head right now), try to keep a certain looseness to drawing creatures, especially when they are in action. If you make too many refinement passes, it can be easy to lose motion, which carries power. Additionally, if you can design creatures to have a flow/rhythm in their attributes, that helps. For example, the feathers here change size in an arc, and the jaw is not the same width through-out; it is variable in width, which is just aesthetically better when you can make it work in a way that looks natural. Which, again, goes back to studies from nature!

Whew, I hope that helps!

Oh, for sure! I'm always happy to help it with insights into process or even direct reviews if people ask, so feel free to inquire any time!