Your indoor trim (crown moldings, baseboards, casings, etc.) can really affect the size, shape and appearance of each room in your home.
Here are some tricks if you want to change it up a bit...
If you want to ENLARGE A ROOM.....Paint the trim the same color as the wall color or just a tad lighter to make the walls feel like they are receding.
If you want to RAISE THE ROOF.....Install crown molding around the perimeter of the ceiling and paint it a darker color than the ceiling to draw your eye upwards.
If you want to LOWER YOUR CEILING....Install a picture rail or a chair rail molding on the walls of the room and paint the rail, and/or the wall area above it a darker color than the rest of the walls to break up the walls and draw the ceiling down.
If you want to HIGHLIGHT AN ARCHITECTURAL FEATURE....Paint the feature, whether it is a mantel, pillar or what have you, a color that contrasts with but is of equal intensity to the walls, this will guide your eye and highlight the feature.
Lastly, If you have natural high quality wood trim already in your room and you don't know what to do.....Just leave it. Leaving the trim in its natural color plays up the beautiful texture of the wood and brings natural warmth and texture to the room.
Don't be afraid to experiment, it's just paint.