There are a couple variations that can be made with the free black/green deck. The deck can be highly creature oriented or creature control heavy.
Cards that specialize in a theme (skeletons and wolves) should be culled out, since the deck would be hard pressed to carry any specific creature theme. Taking out Decaying Hatchet and Llanowar Charm right away.
Keeping the efficient creatures, creature enchantments, and spells, the deck starts to take shape:
Black Knight x2
Soul Crush x3
Llanowar Elf x3
Lone Wolf x2
Giant Growth x3
This selection gives 40 cards to try the deck.
Of course, this is just one deck idea and the deck can either be a green deck with a few black cards thrown in or vice-verse.
Complete black/green list