Depends on what you want to do with the deck. You seem to want to go Aggro based on your title, so any creature 5-cmc and over is immediately out.
More Blood Crypts and adding
Dragonskull Sumit 
s would be good to fixing your mana base. Other than that, 23 lands is about where you want to be, with the Mountain/Swamp split depending entirely on how much Red VS Black you want/need at any given turn.
Now, as far as creatures do, you want a lot of Aggressive cards,
Rakdos Cackler 
,
Grave Crawler 
, basically you're looking at all the 2 power 1 cost creatures in Red and Black. You'll ideally want between 10 and 14 pf them, depending how Aggressive you want your early game VS how much staying power you want.
Stromkirk Noble 
is another to look at because he get's pretty big by just doing what you want to do.
Are isn't much in the way of 2-drops, but Knight of Infamy, Shred-Freak,
Gore-House Chainwalker 
and
Ash Zealot 
are really what you want to look at, with maybe
Crimson Muckwader 
if you're looking to be more heavy into Black than Red. You'll wand between 4 and 8, again depending on how aggressive you want to be early in the game.
3-drops, sadly doesn't have much going for it. Guttersnipe is good if you've got 16+ removal spells for it.
Geralf's Messenger 
if you happen to be VERY heavy in Black. Hellhole Flailer is pretty good if you're a little slower of a deck.
Cryptborn Horror is terrible since you can't play it if you havn't dealt damage that turn.
The top of your creature curve, doesn't have many solid options.
Hell Rider 
is solid, as is
Rakdos, Lord of Riots 
if you have enough guys to ensure you deal damage. Ideally, you'll want
Falkenrath Aristocrat 
whose really strong, but is also a $20 card.
As far as other spells go, Pillar of Flame and Searing Spear are pretty much required as auto 4-ofs. You can run some Dynacharge to pump your horde of small guys, but I like to round it out with more removal.
Stuff like Traitorous Blood is better left in the SB since it's really only needed VS creatures you can't remove or can't trade with favorably in combat/with removal (ie:
Thragtusk 
).
Consistancy is key, which means having a lot of 4 and 3 copies of your more agressive cards, and fewer for cards that you might not what to see in every game, but want to have access to during game 1.
