This may seem obvious, but many people don’t think about it.
Any painting looks best when it’s not competing with wallpaper or some sort of a busy wall.
That’s why galleries are always a neutral white. A simple white wall essentially creates a large outer frame around your painting, even when you have several paintings grouped together. This makes your painting stand out and gives it more importance visually.
Whether your painting is realistic or abstract, colourful or muted, big or small, remember that it loses a lot when it has to compete with its background.