A Simple Design Rule [That Just Might Blow Your Mind]
Use the The 60-30-10 Rule - it states that 60% of the room should be a dominant color, 30% should be the secondary color or texture and the last 10% should be an accent
To choose the three colors for your space, a color scheme based on the color wheel is the simplest method - Monochromatic, Complimentary, Analogous, or Split Complementary
Break the Rule by adding a fourth color, going completely monochromatic, or creating your own formula