An excellent exercise to allow for some creative character designs is to experiment with building the underlying structure from unique silhouettes.
By being tied to using the basic shape underneath it forces us to think about the type of body and personality that might suit for the final character.
Practice generating full characters from as many different body shapes as possible, and experiment between male and female forms.
What is most important is that you remember your characters need physical form and volume, so although the initial starting shape maybe a 2d shape, you need to add dimension to your design otherwise your character will feel flat and lifeless.
You can also apply the same techniques to the head.
This is also an exercise to be found in Disney films where shape theory has been studied an utilised to support the personality of the character, and help define a unique and identifiable silhouette on screen.