Cover the Whole Ceiling
One option that will ensure no one notices your open ceiling is to cover the entire ceiling with a tapestry. General rules of tapestry hanging apply. Choose a tapestry that fits your space completely. Since tapestries can be a bit annoying to hang, the complete covering option is best for a room with smaller and lower ceilings. However, if you have a ladder and a large enough tapestry, feel free to cover the entire ceiling, regardless of height or size.
Since most ceilings have somewhat large surface areas, you may want to use a few different tapestries. Pick tapestries that complement each other and the other designs and colors in your room.
If tapestries are not your favorite decoration items, you can make a collage right on your ceiling. To achieve this, layer posters, pictures, newspaper clippings or a combination of these on your ceiling. While it may seem like a lot of work to cover the whole ceiling for just one or two holes, complete covering will ensure an even look.
Cover Just the Open Spot(s)
Should you not want to go through the trouble of covering your entire ceiling, your decoration solutions can focus on just the open holes in the ceiling. Smaller tapestries or posters can cover just the quadrant(s) of the ceiling with hole(s). If you want to cover an even smaller area, you can place a ceiling dome or medallion directly over the hole. Medallions and domes work best if your hole is closer to the center of the ceiling. An off-center dome can be just as awkward as a hole.
If you don't want to add additional items to your ceiling, consider taping over the hole with masking tape. After you tape the hole, paint the tape the same shade as the ceiling. While the tape solution isn't full proof, most visitors will probably not notice anything out of the ordinary.
Working with the Open Spot(s)
If you're adventurous, embrace your ceiling holes. With the use of paint, you can incorporate the hole into a ceiling mural. For instance, paint the area around the hole to look like a dirt mound. Then the hole becomes a rabbit hole instead of a gaping ceiling wound.
Another option is to use a sanding device to make your ceiling holes rounder. Then you can paint a pattern around the hole. A series of rings or rays emanating from the hole will add a geometric personality to your ceiling.
Finally, consider hanging items from the hole. Just like some people hang strings of beads from their door frames, you can hang beads from the hole in the wall. If you want symmetry, then create a second hole on the opposite side of the ceiling and hang beads or streamers from the second hole as well.