Hello everyone!

Here's a deck I've had reasonable success with so far (somewhere around 70% win) in plat 3. I'm looking for constructive advice on how to fix it, improve it and make it a better deck overall. I don't have many epics (none), and my library isn't exactly loaded with rares, but...in case there is something really awesome i can do with this baby, I'm all ears.

Sneaky Spell Damage Deck:

2x Backstab
1x Preparation
2x Sinister Strike
2x Deadly Poison
1x Betrayal
1x Eviscerate
1x Sap
2x Shiv
1x Bloodsail Raider
2x Kobold Geomancer
2x Novice Engineer
2x Fan of Knives
1x Headcrack
2x Dalaran Mage
1x Si:7 Agent
1x Ogre Mage
2x Assassin's Blade
2x Assassinate
1x Archmage
1x Sprint

I was actually thinking of putting a couple of mana wyrms in there, but don't think that would work. I got badly beaten by a rush warrior deck once, had a bunch of bad draws vs one mage (no creatures on my part), and a pally with no cards pulled out a divine favor one turn before i was about to finish him off. All in all, I'm surprised how effective the deck has been so far, but am more than willing to listen to more experienced player's advice!