To add realism to your scale miniature poinsettia leaves you should draw in light vein lines with a pencil or colored pencil. There is a vein line down the center of each bract and leaf which is usually a slightly darker green than the leaves. Side veins go in a slight curve out from the central vein to any points on the sides of the leaf or bract.
You can shape the leaves to make the veins more realistic by pressing a fine ended embossing tool down the length of the vein while the leaf or bract is sitting on a soft surface. I used an eraser but craft foam or a mouse pad works as well. If you don't have an embossing tool, use a blunt crewel or darning needle, or an empty cast off ball point pen.
Shape all the leaves and bracts you have cut, and sort them into a rough range of sizes, from small to large (by length).
If you wish to make your poinsettias have the velvety texture of their real counterparts, apply a fine layer of artist's chalk or pastels to the upper surface of each leaf or colored bract after you have finished applying the veins. Experiment with different colors. Burgundy or pink chalk applied to the centers of white bracts will make different colored plants than the standard red variety.