This one is, Don't be ruled by your photographs! Even if you frame the perfect view, there's bound to be something about it you don't like--the light, the shadows, the composition--how did that building end up falling dead center in your composition? That tree is too dominant over there at the edge of the page without something to balance it. There are too many people in this landscape. There are too many details in this city view. Bottom line is, if you are an artist, you may not be a photographer, and many times you are snapping reference photos with your smartphone, so remember that the pictures are for reference and don't let them call the shots.
To emphasize this, Brenda gave us a scene with a lighthouse attached to living quarters, with some pine trees, and water, and rocks. Then she had us separate out all the elements--trees, rocks, lighthouse, sky, water--and recombine them into a composition we actually wanted to paint. It was a great lesson! Here are my thumbnails, with notes: