How do I make this pose look less stiff and more fluid?

[proud parrot]

I need help making this pose more fluid and less unnatural

[jagged island]

The easiest solution for you will be using this as heavy reference ^^

That mean, you will trace the pose to have better understanding about human joints and how they bend. As long as the traced art used for learning material, there is no need for worrying copyrights or such.