- Learning to draw is not actually so much about drawing, but learning how to see. Light is complicated and humans like to abstract, especially geeks, so when we look around, we rarely actually see what's there. When you look at e.g. a shiny teakettle, you need to see the specific reflections in the metal, rather than just parsing it into "shiny bowl". When you look at faces, you need to learn to spot the shadows and the curves from various angles, e.g. a face in profile vs a face head on. Even simple objects can be deceptive, e.g. put a box on a surface, and it will create a subtle border of shadow around its base due to indirect light bounces. I found drawing from photographs was best for learning this, as it's pre-flattened into 2D. Also, there is a reason that artists study the anatomy of skeletons and musculature to draw nudes.

- To make matters worse, our eyes and brains suffer from various optical illusions. This means that you should not strive something that is right, but something that looks right. For example, horizontally aligning an asymmetrical shape... sometimes it just looks more balanced slightly off-center. Or go into Inkscape and type the text "XOXOXO". Zoom in, and you can tell that 1) the X' diagonals don't meet at a central point and 2) the O sticks out a bit below and above the X. Both are there to 'fix' optical illusions. Also, because of the difference between left brain and right brain, often it helps to flip your image horizontally midway to see all the flaws.

- When it comes to design (rather than just art), the motto is "it is perfect not when there is nothing more to add, but when there is nothing left to take away". This can make it hard to see why a design is good. The best way I've found is to try and copy an existing design, but only by studying it once at the start. When you're done, you can compare with the original, and suddenly all the artists' specific choices will stand out. Doing this to CSS Zen Garden designs taught me web design.