Such wealth of information is available by reading and by simply looking at great art.
Stapleton Kearns offers amazing information on his blog, and I have lifted this list of plein air painting issues he has noted are of consistent concern to his students.
Lane's Island Surf, Vinalhaven
Yes, I have edited this list a bit, and added comments. Refer to his blog post here for the original, and to find a plethora of amazing information from this stellar painter.
Plein Air Faults, originally by Stapleton Kearns, with my notes:
The painting is in all middle values with the contrasts so suppressed that the painting has no punch.
The values of the lights are confused with the values of the shadows. The lights are not consistently brighter than the shadows.
(Considerate planning and looking can fix this error. I often rely too much on instinct when painting but am now making an effort to plan more at the onset of a new work.)
No attention paid to color temperature. The picture is executed with no regard for which notes are hot and which are cool. This is particularly true with painters using three color palettes, which don't lend themselves to the expression of color temperature.
Drawing is haphazard or done without much care or delicacy.Often this happens to painters who value velocity or brushwork over drawing. Usually painters with studio backgrounds, or better still, atelier training seem to have a better grasp of drawing the landscape.This is a failure to look very closely at the landscape.
(Drawing is important, surely. I am not so disdaining of artists who 'value velocity or brushwork over drawing' but for me, that is up to the painter.)
Designs that are overly symmetrical or too"stock".
An uncomfortable closeness to the nearest objects in the painting.
(Sometimes this is truly effective in pushing the space in a work. My students hear about this all the time during my critiques of their work.)
A line which seizes the viewer in the foreground and directs them into a collision with the side of the frame rather than into and through the picture
An underpainting in a hideous and assertive color that poisons every note laid on top of it. This is usually explained as something a previous teacher ( who was REALLY good!) had insisted was the only way to do things.
(I may be an advocate of this 'hideous and assertive' underpainting color. I like it!)
Every color in the painting is as bright and saturated as it can possibly be painted.
A cursory "that's good enough" effort without a real intent to create something special. The painting is banged out in a short period of time and without much reference to nature or an attempt to design or bring anything personal or original to the presentation.
It's a great list with tons of food for thought.
When I'm at my sketchbook, I'll be considering all of it!