There's a cool book called the manga matrix. it breaks down creature and character design into a grid and it really helps put everything into line...at least for me when I was starting out with it. Now, I just collect a crap ton of references from the internet and literally do trial and error.
The problem you are having may be related to a limited visual library. It isn't related to lack of technical skills, but more that your internal database may be lacking in terms of design. The video also has some helpful tips on how to fix that aspect if that is indeed the problem you are having.