Start with a foam mannequin head. Use a craft night to make a hole along the crown so that you can get dirt and plants inside.
Once you have your hole you can paint your sugar skull. More is always better. I even added some sequins for sparkle.
I filled mine with succulents, but flowers would also be amazing. Marigolds and Day of the Dead go hand in hand. You could also use fake flowers. I myself am a succulent kinda gal and adore the way this beauty turned out.