I started playing near the end of February and have built a few decks that have beaten my more experienced friends' decks, while also getting destroyed by them. The one I have put the most love into is one that plays with the graveyard (Entombs and whatnot, however this makes me very nervous when I play with it. I destoyed my friend, as hard as he tried, but screwed up in the next game by not realizing my Archfiend of Depravity could have saved me from his steadily growing army o/ myr tokens. Obviously, it requiring a graveyard, cards like Crypt Incursion can put me in my place. I feel my biggest issue is not having enough of the same card. I guess I have it like that because I want to see how certain cards work. That being said, my lack of knowledge of the game and of cards has been a nuisance, so I would like some advice on what to do with the following library.

Green Creatures (9)
1x Wasteland Viper
1x Deadly Recluse
1x Satyr Wayfinder
3x Eternal Witness
1x Nylea, God of the Hunt
1x Hornet Queen
1x Terastodon

Black Creatures (12)
2x Doomed Necromancer
1x Hidden Horror
2x Gatekeeper of Malakir
2x Geralf's Messenger
1x Sibsig Host
1x Archfiend of Depravity
1x Grave Titan
1x Avatar of Woe
1x Spirit of the Night

Black Spells (16)
2x Dark Ritual
1x Disentomb
2x Entomb
1x Unearth
1x Zombie Infestation
2x Animate Dead
1x Ultimate Price
1x Shallow Grave
1x Murder
1x Necromancy
1x Victimize
1x Buried Alive
1x Diabolic Tutor

Green Spells (2)
1x Mulch
1x Evolution Charm

Gold Spelol (1)
1x Jarad's Orders

Lands (20)
7x Forest
8x Swamp
3x Jungle Hollow
1x Urborg, Tomb of Yawgmoth (not exactly sure why)
1x Evolving Wilds

Basically, I try to put the heavier cards in my graveyard to pull them out for cheap. I have a lot of cards (Buried Alive, Dance of the Dead, Reanimate) in my "sideboard" that play with this, and some I would like to throw in (Amulet of Vigor with Victimize or Geralf's Messenger could be fun). Also, I figure I should play with the non-basic lands. I've seen other cards that I would like to at least get a hold of. So, suggestions are more than welcome. Please and thank you.