Hearthpwn

This is my Standard Dragon Priest deck (pre-ONiK) that I have been refining since before WOTOG. It uses dragon synergy to play minions ahead of curve and out-value your opponent. This is a tempo deck, so maintaining a consistent curve is extremely important. If you curve out perfectly many decks will be unable to keep up. 

Perfect Curve

T1: Twilight Whelp (or Northsire Cleric)

T2: Wyrmrest Agent

T3: Blackwing Technician

T4: Twilight Guardian

T5: Blackwing Corrupter (Holy Nova vs Zoo)

T6: Cabal Shadow Priest

T7: Heal+Azure Drake

T8: Forbidden Shaping

T9: Ysera (if they are out of removal) or Nefarian (for card draw)

T10: Heal+Forbidden Shaping

Strategy

If you have no other dragons in hand, save a T1 Twilight Whelp. A 1 mana 2/3 is good but keeping a dragon activator in hand and playing nothing T1 is usually better.

Forbidden Shaping is in the deck to round out turns where you can't stay on curve. When you can't play the perfect minion, play a cheaper minion+removal, or play Forbidden Shaping. A T8 or T10 Shaping can be quite good, but keeping the tempo up is much more important, so Shaping keeps the pressure on.

Against C'thun decks ALWAYS save either Entomb or SW:D for use against the big guy.

Tech cards and Substitutions

Forbidden Shaping, Shifting Shade, Entomb, and Ysera are all fairly flexible.

Forbidden Shaping is good to round out sub-optimal turns, but not strictly necessary.

Shifting Shade is a solid mid-game minion, but could be swapped for more removal, usually either another Entomb (vs Control) or another Excavated Evil (vs Aggro or Zoo). Card draw in the form of Thoughtsteal could also take this slot.

Ysera provides a big, late-game threat (and is my personal favorite card in Hearthstone!), but any big dragon could do. Against faster metas she can be removed in favor of something smaller like Fairy Dragon or Dragonkin Sorcerer. 

Chillmaw deserves special mention as the one card I don't have that has the potential to really buff this deck against aggro. The taunt stops the onslaught, and the deathrattle can be devastating.

Mulligan Guide

Ideal Starting Hand: Twilight Whelp, Wyrmrest Agent, Blackwing Technician, (Twilight Guardian)

Keep your Whelps pretty much always. I normally keep Northshires and Wyrmrest Agents, as well. If you draw a higher mana dragon and no good early game minions, keep the dragon and redraw the other cards. Keeping a dragon activator in hand is essential. Against Warlock or Shaman I usually keep a Holy Nova or Excavated Evil.