The first thing you should do is create a model. The size should be bigger than the final size, because after several firings, the clay will shrink. You should keep this in mind. If this is a figurine, then it could be sculpted in clay. For small and medium-sized objects, such as mugs and coffee cups , I draw them using 3D software and print out on a 3D printer. Occasionally I ask my ceramic friends to make models on a potter’s wheel. In any case, the first thing you should do is create a “rough” model which you should grind, copy with the silicone mould, refine it, and finally get the final product.