To successfully stencil, use fabric paint or thickened dye. If the dye or paint is not thick enough, it will seep under the stencil and ruin your design. You can use commercial stencils or cut your own designs.
Use hard rubber stamp, wood or metal to emboss with.
The image you are embossing will need to withstand heat and steam.
Lightly spray the pile side of rayon velvet with spray starch.
Place face (pile side) down onto the stamp or embossing image.
Press firmly with an iron set on medium heat.
Do not wiggle around too much or you will get a blurry image.
Set aside to dry thoroughly.
Note: this is not a permanent technique. If you wash it the image will probably blur or disappear.