Here is an example of painting with gusto and keen observation. What is particularly interesting to me is the subtlety of the late afternoon light skimming the shrubbery and illuminating the statuary. This is why value is so important. The strong contrast of the dark trees behind the light sculpture invites the viewer to be drawn to the center of interest. The eye is always drawn to the greatest contrast. Note also the dark mass of the foliage is composed of subtle value changes. This is to prevent boredom.
If you look at the lady carrying the child and run an imaginary line horizontally through her eyes, you will have established the horizon or eye line. The two statues are the same size but one looks smaller due to the laws of perspective. Again, draw an imaginary line from the top of the head of the near statue to the top of the head of the distant one. You will notice that the line you have drawn intersects the horizon line near the ladies on the park bench. If you draw another line from the base of the statues, it will intersect the eye line at the same point as the line you drew from the top of the heads. The point of conversion is called the vanishing point.
What makes this painting work is his wonderful use of warm and cool colors and his absolute mastery of value. If you examine this painting, you will notice there is very little detail. Sargent, looked, noted the shape, the hue, value and he put it down on paper. As a result, this painting is made up of many accurate tonal notes. This translates into a beautiful painting that communicated the intent of the artist.
If you stop and examine carefully the paintings of Sargent, you will see those principles I have just discussed. Be aware of the values, the and composition. Try and apply these principles to your own work.