3. Create illusions.
Paint can be a powerful ally for making architectural details you don't like disappear. Erase them by painting them the same colour as the walls. Conversely if you want to make anything stand out, do it subtly by using a stronger tone, or really make it pop by using a different colour. This works the same with furniture. You can use colour to cover but also to make aspects of the room sing. If you have a piece of art that you want to stand out, pick a dominant colour from the picture as its backdrop, instead of white; but if you have a large practical item of furniture like a wardrobe, reduce its visual dominance by painting it the same colour as the walls.