Refrain from mixing colors. The colors should be bold, vibrant and pure. Avoid using black. When you need a darker color for shadows, use contrasting colors together.
Use thick, raised short strokes that stand on their own. The strokes should give a sense of texture that mimics the subject.
Play with the natural light on your painting. Outdoor scenes were very important to impressionists, and they made the most of the sparkle of light and the splash it gave their paintings. Give shadows interest by making them darker versions of the painted object.
Establish an asymmetrical balance by arranging the elements to allow the eye to naturally move around the canvas, instead of being directed toward a central point.
Pick a subject depicting everyday life instead of an arranged, artificial setting. Outdoor landscapes, crowded scenes with many points of interest and city streets have all been successfully used by impressionist painters.