There are a couple variations that can be made with the free blue/black deck. The deck can be highly creature oriented or tactically crafty.
Cards that specialize in a theme (rouges and skeletons) should be culled out, since the deck would be hard pressed to carry any specific creature theme. Taking out Nimble Dagger and Decaying Hatchet right away.
Keeping the efficient creatures, creature enchantments, and spells, the deck starts to take shape:
Sentry Rogue X4
Aura Finesse x1
Time Ebb x3
Black Knight x2
Zombie Grunt x3
Soul Crush x3
This selection gives 40 cards to try the deck.
Some of the less efficient creatures (Obsidian Golem and Sentry Rogue) can be switched out for more crafty cards (Surgical Precision, Royal Assassin, or Call of the Reaper) or better cards from the free booster.
Of course, this is just one deck idea and the deck can either be a black deck with a few blue cards thrown in or vice-verse.
Complete blue/black list