If you're painting an entire room, first paint the ceiling, then the walls. It's also usually better to paint large areas
like walls before repainting the trim; because you'll work more quickly when covering open areas, this can result in roller
spatters, overspray and occasional errant brushstrokes.

Many homeowners paint the walls first, then move on to the trim while they wait for the first coat to dry. Homeowners should
 think more strategically, says Rich O'Neil of Masterworks Painting. "Paint all the woodwork first—the first and second coats
—then move onto the walls," says O'Neil.