Hearthpwn

This is the deck I've played most over the years in some iteration. I love the resurrection mechanic and find it really fun to play.

The trick with big priest is patience in early game, while preventing yourself from dying having played no cards... It's not until turn 6 we can start scaring people.

Board clears galore: we're running Excavated Evil to deal with small minions on turn 5. Just heal yourself with hero power up until now. This card also jumps into your opponent's deck to give them a potentially useless draw later in the game, since most of your minions later will have more than 3 health. Mass Hysteria is another decent clear if you have no minions, but you need a bit of luck. Look to use this when all enemy minions have higher attack than health. Psychich Scream can save your life. Only use it if they have lethal next turn. You might have to gift them one of your own minions but you might have a chance to swing it next turn with cards like Mass Resurrection and Lesser Diamond Spellstone. Plague of Death obviously isn't a clear for the early game, but it's nice to have should you need it very late on.

Mulligan hard for:

Archmage Vargoth: low cost card, high value target to save your face. He's basically a taunt. You'll get him back later.

Mulligan medium for:

Forbidden Words, Shadow Word: Pain, Shadow Essence: 2 early removals for annoying early enemy minions, and Shadow Essence is your best chance at getting an early 5/5 Rag, Statue, Zilliax or Lich King.

Mulligan low for:

Zilliax: Lowest cost minion except for Vargoth. Lifesteal needed early game usually. Excavated Evil, Mass Hysteria.

The general idea is to get your big minions on the board, do some damage, get them killed, resurrect them. Overwhelm the enemy. You'll be playing a lot of spells to build up your Lesser Diamond Spellstone. This in turn will discount the cost of your Grave Horrors.

Keep count of how many minions you have in your death pool. If you have Archmage Vargoth, and one other minion in your death pool, try to make Kel'Thuzad the third. Play Mass Resurrection on your next turn and you'll end up with 2 Vargoths, 2 Kels, and 2 of another good minion.

Have fun playing, it's not easy to begin with. Let me know if you have any questions!