Little tip from myself.
You have to change point of view, try to look on the 3D effect not as a whole but as scale, rotate, move etc. Try to see which element and how would be moved by scaling, rotating, translate tools which you can use in 2D. In fact using those tools, parts, you can build illusion which well folded gives the 3D effect 🙂 It really helped me when I changed perspective.
