First, when you have the shoes you want to decorate, you need to spray paint them the base color that you like. I would not recommend painting the inside of the shoe because it wears off. Put some paper inside the shoe while you spray paint the outside.
After the base paint is dry, I made a stencil for the sparrows and I made a rough outline of all the sparrows I wanted on the shoes. If you do not use the silver Sharpie and your base color is black, you are going to have to do multiple coats of the paint for the sparrows. I HIGHLY recommend using the Sharpie first. :)
For the straps, I just sewed tubes of fabric with an angle at each end so that when the tube/straps are tied on the shoe, it looks like a bow. I then painted the sparrows on the straps and then stitched the straps to the shoes.
After everything was done and painted, I decoupaged the outside of the wedge so that the spray paint was not sticky and would not attract dust.
Good luck!!! :)