Look in the big shops for the brand magic sponge its a small white block,
I cut it up in portions add a little water to it and apply even pressure this has never let me down.
I have in the past used a cutting paste you use on cars, don't worry about it going dull, clean spotless and spray with acrylic clear lacquer evenly you may have to spray twice depending how clever you can be. Its important you have a warm area and the surface is warm to prevent any runs do a practice run on a dummy plastic till its right, make sure you have plenty of ventilation and a mask its not advised to breathe in these fumes,
I hope this has been some use to you,