There are a couple variations that can be made with the free black/red deck. The deck can be highly creature oriented or tactical spell heavy.
Cards that specialize in a theme (skeletons and goblins) should be culled out, since the deck would be hard pressed to carry any specific creature theme. Taking out Decaying Hatchet and Super Swift Boots right away.
Keeping the efficient creatures, creature enchantments, and spells, the deck starts to take shape:
Black Knight x2
Zombie Grunt x1
Soul Crush 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 red deck with a few black cards thrown in or vice-verse.
Complete black/red list