There are a couple variations that can be made with the free white/black deck. The deck can be highly creature oriented or enchantment heavy.
Cards that specialize in a theme (soldiers and skeletons) should be culled out, since the deck would be hard pressed to carry any specific creature theme. Taking out Helm of Fortitude and Decaying Hatchet right away.
Keeping the efficient creatures, creature enchantments, and spells, the deck starts to take shape:
White Knight x2
Black Knight x2
Zombie Grunt x3
Soul Crush x3
This selection gives 40 cards to try the deck.
7 cards have 2 black mana in their casting cost, keeping black as the majority is good.
Of course, this is just one deck idea and the deck can either be a black deck with a few white cards thrown in or vice-verse.
Complete white/black list