One painting technique to strengthen your painting composition is to look for opportunities to create right angles by adjusting the slants of shapes in your painting.
This painting by Jean-Francois Millet uses this techniques. The figures are at right angles to the horizon line.
Here is an example of the principle of right angles in a painting by Arthur Streeton. He carefully angles the tree to be at right angles to the position at which it crosses the top edge of the field.
Here is another example of the compositional principle of right angles in a seascape by Winslow Homer. He angles the dress of the figures to be at right angles to the slanting rocks. He also lets the figure cross the horizon of the sea to create a another right angle.
