This demonstration illustrates a few concepts of putting a sense of space in your paintings. Begin with the sky, a darker value at the top getting to a lighter value at the horizon. Place the horizon a little lower or a little higher than dead center. Putting the horizon in the center does not make an interesting painting. Think of the 3 bears when composing the size of the 3 main areas of a painting, have a large Papa bear, a medium size Mama bear and a small Baby bear to make it just right. Here I have the sky as Papa, the sand/sea as Mama and the figure as the baby.
The ocean starts darker lower in the painting or the 'closest' inland and gets lighter at the horizon. But at the horizon of the sea or very large body of water, has a darker line.
The sand is darker at the bottom of the canvas and gets lighter towards the horizon, except if it is getting wet from the water, then it is a darker value at the water's edge.
Remember, these value changes do not have to be drastic, they can be baby steps of changes - but need to change some in order to create the sense of space.
The figure wrapped in the blanket is sitting, so there is a shadow under them. The cast shadow on the sand should be darker than it is.
The important part of the demo is the size of the figure. The number 7 is the magic number of the human adult figure. The average size of the figure if 7 heads. determine how tall the head is and the size of the upper torso from the waist to the head is about 2 heads tall. The lower torso is about 1 head length and the legs are about 3 head lengths longs. Even when you are painting an indistinct figure in the landscape, if you follow these proportions your figure will look realistic even if you paint it with just a few strokes.
Put people in your landscapes to add life to them - just keep the 7 heads in mind.