When you have short ceilings, it's easy to feel claustrophobic. Paint the ceiling trim the same color as your walls to make the ceiling look higher. Painting the trim this way provides an optical illusion that extends the length of the walls. This is an especially good idea if you are painting the walls and ceiling two very different colors.
Much like painting the trim the color of the walls, if you paint it the color of the ceiling, it will make the entire room look bigger. It provides an optical illusion that shows the ceiling getting bigger. Paint your trim the same color as your ceiling if the room in question is smaller and doesn't have a lot of floor space.
You may have chosen contrasting accent colors for aspects such as door and window trim. In this case, paint the ceiling trim in this accent color. It will tie in the contrasting color from floor to ceiling, and will look especially pleasing if you've also painted wainscoting in the contrasting accent color. For instance, you may have painted your walls a deep red and your window trim a neutral beige. Bring this beige to the ceiling trim as well.
Although painting the trim to match your ceiling, walls or accent colors is a practical approach, you may want to be more creative with your paint color choices. Choose a color that's completely different than any of the other painting colors you're using, but that may tie in colors from your furniture. A flash of bright pink will bring your eye to the ceiling every time. You can also use faux finishes and even stamped paint designs to add whimsy to your ceiling trim.