It largely depends on what style you draw
If it is anime style I usually recommend to copy it from other pictures because there is no point to draw same thing over and over again.
Also copying stuff in general is pretty good way to learn.
Other artists recommend learning perspective anatomy and other stuff, but I am engineer and thus I treat everything as collection of components and sub components which you have to assemble into desired product.
The more components you learn the better is your "product"