Ask an Artist, What nuggets of information have helped you the most in your understanding of painting?
Gosh, that’s a great question. I think there are two nuggets that I got while learning to paint that really helped me turn a corner or two.
The first would be the idea of John Carlson’s Value Planes and Subsequent Values. Just understanding the approximate values of the big planes of the landscape (sky, ground, slants and uprights) helped me to simplify the landscape into its most basic planes. It also helped a ton when I started doing the urban landscape and still life. The biggest trick to it is knowing that you have to keep an open open eye and know that it is a principle and not a law. It’s our job to observe what it is we are painting and to figure out what the two darks are and what the two lights are. If it was a snow scene the ground plane may be lighter than the sky plane… or if the sun is just come up, an upright could be the lighter light. I think the big takeaway is to observe what you are painting and edit it down to the 4 simplest masses.
“ Every good picture is fundamentally an arrangement of three to four large masses - a design of differing masses or large blocks of color- light, dark and half- dark and half-light. Any detail or embellishment placed within the big masses is so subordinated that it is in no way disturbs these masses. “ John Carlson from Carlson’s Guide to Landscape Painting

Above: This is by far my favorite illustration of Carlson idea… showing the different planes and generally where those planes can be found on the value scale. Very helpful!

Images from https://thelandscapeatelier.com/2021/01/01/carlsons-theory-of-angles-an-introduction/
As an even more simple bit of information, I would say the idea of the notan was a huge game changer for me. I have been into art my while life… 4 years of art school, some post-grad work and 25 years of teaching and I had never heard the term “notan.” I can’t remember when I heard it first or where, but it was during a workshop. Being able to see your subject in terms of the patterns created by the light dark family is very powerful… two simple shapes. Squinting will help you visually to isolate and identify the average dark shape and the average light shape.
From Wikipedia:
Nōtan (濃淡) is a Japanese design concept involving the play and placement of light and dark elements as they are placed next to the other in the composition of art and imagery.
Here's a scene I used for a gouache sketch:

Here that scene is in a quick notan done in Procreate:

Gouache Study:

Both of these ideas are worthy of deep investigation. This was the tip of the iceberg. For more reading: Carlson's Guide to Landscape Painting, Composition: Understanding Line, Notan and Color by Arthur Wesley Dow , Kevin MacPcpherson's Landscape Painting Inside and Out.