For monsters, I'd leave it up to imagination to decide on the outcome.
The fun part about designing a creatures is taking risks. Not every design will always make
the cut but it opens up new possibilities.
Drawing humans are fine, but sometime can get dull and boring since there is a norm already set in stone with fundamentals to follow. (I remember those dreadful college days at art schools)
With monsters there are no rules to follow.
When I have something fleshed out, one question I ask is "How can this design interact with the characters in the story"
One method that is normally used by many is meshing one, two, or multiple existing designs together. Or basing things off inanimate objects or things organic and living in nature. Lines and shapes are your best friends.