Once the leaf is drawn, start shading it. Zig-zag patterns are used to shade the leaf. Divide the leaf into two sections by drawing two parallel lines and start shading the leaves. To get a complete picture of the mehendi, you should look once it is finished, see below

You can see how the leaves are shaded differently. The leaf on the top of the flower is divided into two sections and then the shading is done. The bottom leaf has shading on all its sides and then a small petal like design is executed in the middle. This design is so simple that it can be done on the palm and also on the arm as mehendi tattoo.