Use the golden ratio when planning your painting composition.
Author: Sonia Reeder-Jones
These lines divide your canvas into a 1 : 1.618 ratio which is referred to as the Golden Ratio. One side of the line represent 1. The area on other side of the line should equal 1.618 or 161.8% of the opposite side.
Consider placing the focal point of your composition near the point where the horizontal line and vertical line intersect.