This is a collection of images, found all over the internet over the course of years, containing useful guidelines by professionals for people who want to be professionals. Credit will be given when possible.
These aren't "how-to" tutorials. There's no step-by-step instructions for how to draw. They're mostly about changing the way you think about your process. There's a few anatomy guides, but nothing should be taken as a substitute for life drawing and practice.
Most of the animation guides can also apply to comic book art, which is really the focus of this collection.