2. Always always always ask youself "WHY?". I feel, quite strongly, that this is a fundemental element of understanding and creating art that is sorely overlooked in today's art education venues. Too much focus is placed on HOW to draw/paint but not nearly enough placed on WHY, the how works.
For example, anatomy. There are fundemental rules to how the body is put together. Bones act as anchors for muscles which move the limbs which deform the skin which makes the body look like it does in whatever position it's in. Yet, in most anatomy classes emphisis is placed on different ways to draw the body as an object sitting in front of you rather than the intricate machine it is. Without that underlying knowledge of that machine that fills that structure you're simply copying a visual reference. Take away the reference and you've got nothing. Learn the WHY e.g. why does the body look this way when I put my arm up... And you can make educated and informed decisions when looking at a reference, advance more quickly in your understanding and ultimately be able to understand what you're viewing to the point where you can intrinsically be able to reproduce it without the reference.
And that's just one example. Everything about the images you create, composition, psychology, anatomy, costume, architecture, perspective, camera angle, color choice, lighting, EVERYTHING has an underlying and oft times dynamic set of "rules" that determine it's success in your drawing which in turn determines the success of a particular piece of art. Understand those rules, or more simply put, WHY something works or doesn't work and you can create art with forethought and intent.
Think of it as the difference between walking into a room with a gun taking careful aim and shooting at a target rather than, walking into a room, closing your eyes and shooting in the general direction of the same target. Chances are you'll hit a lot more often doing the former.
These grapes taste like Fresno! -- Steinbeck