I have tried cosmetic and dish sponges and prefer the cheap dish sponges, for me the cosmetic sponges soak up too much of the polish. All I did was pull out OPI Big Hair, Big Nails and applied a small amount to the sponge, then I took my base colour, Orly Crush on You and applied another small amount right beside the other polish. I then lightly dabbed this on the nail concentrating the pink at the top of the nail.
Once the first layer is dry, repeat the same process until you are happy with the saturation of the gradient. Add a layer of top coat to smooth everything out and you are done! I would recommend a thick layer of topcoat to smooth over any texture that was created by the sponge.