When you say "randomly" do you mean that you want them sprinkled on the top they way they are in the picture? If it is then I would frame them with the background fabric to create blocks that are uniform in size then you can just piece them with the background fabric and they will float they way they are in the picture.
Or you could make them the centers of stars (super fast with HSTs). Applique is a good option, too, as Yosamitesa suggested. I'm not good with applique so I always go for the piecing option.