1. Purchase at your local craft store, a piece of green or white styrofoam (the floral styrofoam works fine, or the harder craft- it doesn't matter).
2. Spray paint the styrofoam with black or grey spray paint.
3. Buy or make grave stones and other halloween decorations. Cover with cobwebs and whatever spare decorations you have lying around (spiders etc).
4. Make Jack Skellington cake pops (tutuorials available on the web).
5. For more stability, and ease of transport, I place the styrofoam in/on a tray!
Voila! Have fun.