The blank wall is a problem my clients constantly want help with. Many seem stuck on the idea of finding one huge piece of art to fill a wall. An easy way to sidestep this issue is to take a group of photos or pieces of artwork that you already have and hang them together.
An interesting grouping of pictures reads like one larger piece of art. The way that you hang them can be very dynamic and you can change the look of a wall while holding on to your favorite art or photos by just rearranging the pattern of frames.
My artist niece, Katie pulls this off with her usual flair. Pieces that are fine by themselves are more engaging as part of a larger work. The whole grouping draws you in.