This deck is predicated on having several big value packages that work in tandem, as well as taking advantage of some of the sweet new mechanics from Scholomance.
It begins with the Galakrond shell, which of course means lots of cheap and efficient boardstates with all of your invoke cards. I find that the cheap demons and minions combine beautifully with your Lackey package, as you always have room to play between creating lots of minions and making good trades. Plus, Plague of Flames is stellar with both of these card-sets, as you can deal with almost any board for relatively low cost.
Expired Merchant can seem a little strange without Hand of Gul'dan, but trust me it wins games. Use it to discard either Galakrond, the Wretched or Kronx Dragonhoof and then instantly kill it with either Plague of Flames, EVIL Genius, or even School Spirits. As a bonus, you can use the rush lackey to trade it into something for a quick 3 damage. Doubling up on your Galakrond or Kronx can easily put you over the top.
Your lackey cards are obviously best after you've played Dark Pharaoh Tekahn, but don't be afraid to just play them in the more aggressive matchups. The same goes for Grand Lackey Erkh, don't hold it if you're going to start hemorrhaging life. The grand lackey is best post-pharaoh with a single lackey, an empty board, and ten mana to just blow people out lategame, if you can swing it. Keep your hand-size manageable when using grand lackey so that the byproduct cards you discover from the spell and dragon lackeys don't cause you to burn cards.
Soul Fragments help you stay afloat against midrange and aggro, just be sure to try and manage them in the control matchups so that you can always have one in-deck for your Void Drinker. They allow you to life tap more aggressively sometimes, and against aggro can be gamechanging when you have six in your deck and play a Veiled Worshipper. You need the removal cards from this package as well.
Mulliganing can be hard with this deck, since you're trying to develop enough invokes for a good Galakrond and also needing to eventually get lackeys going. Against aggressive decks like demon hunter, pure paladin and painlock, try for your soul fragment cards like Soul Shear and cheap invoke cards. Lackeys are less consistent, but do often work to contest the board if you don't get exactly what you're looking for. Against slow control decks, try to be the agressor and set up huge swings like a fully invoked Galakrond or dropping a Dark Pharaoh Tekahn onto a board full of 1/1 lackeys. You force these decks to use up a lot of removal with your invoke cards, so sometimes you just run them into the ground. I've won multiple priest matchups lategame just because I saved one 4/4 lackey and a Grand Lackey Erkh for after they'd wiped my board, creating a huge 4/4 board and netting extra cards. You have to be disciplined with your deck total and try to avoid tapping unnecessarily, since Veiled Worshipper can drain you pretty hard.
It's a deck with a ton of room to maneuver, but does take some practice to play properly. If you like lackeys (old rogue players, looking at you) and enjoy deep lines of play this is the deck for you. I'm diamond 4 and climbing right now with a decent winrate, after having tried several different iterations and arriving at this one. Enjoy!