Make a border around the edge of the ceiling. Start with string lights (often called Christmas lights or holiday lights) and long lengths of tulle. Pin the tulle on the ceiling side of the seam between the ceiling and the walls, placing a pin every foot for a tighter tulle or every few feet for a loose, draping effect. Once the tulle surrounds the entire ceiling edge, repeat the process with the string lights so the string lights will be highlighted against the tulle. Alternately, place the lights first, and pin the tulle over it (not touching) so the lights will make the tulle glow softly.
Create a night sky effect in the room by placing dozens of tiny light sources on the ceiling, then hanging sheets of tulle across the width of the room. String lights are likely the most time-effective way to place that many small lights. Attach multiple strands of string lights flat to the ceiling in a random, scattered fashion, creating areas with many clustered lights and areas with few lights, the same way stars are scattered throughout the sky.
Conjure an exotic atmosphere, like a cross between a Marrakesh marketplace and an Arabian palace, with red tulle and a selection of hanging Moroccan lanterns, oil lamps and candle holders. Start with large amounts of red tulle. Gather lengths of it in bunches, and pin them to the ceiling, retaining the folds and uneven dimensions until the entire ceiling is covered. Install discreet hooks amongst the tulle. Hang a lantern, lamp or candle holder from each hook to complete the fantastical look. Add an electric-light chandelier or lamp to the array if desired.
Make the room feel like an undersea palace with iridescent blue and green tulle, multiple lights and seashell and pearl accents. Start by installing an overhead light fixture on a dimmer switch. (The single light source will evoke the sun shining above the water's surface.) Hang iridescent blue and green tulle across the ceiling with slight draping between each pin to evoke the ripples and waves of the sea. Place lightweight accent pieces like seashells and pearl-like beads in the "slings" created by the draping tulle.