Details. Details, Details.
Choosing the right sheen can enhance color. Painting the walls in a gloss will add dimension and levity. Semi-gloss on a low ceiling will move light around the space and create the illusion of height. From a practical standpoint, remember that shinier finishes look best on smooth, well-prepped (e.g. spackled, sanded, etc.) surfaces, while matte or flat paints are more forgiving of imperfections.