Hearthpwn

The goal is to keep the board full with any size bodies to later be buffed. Echoing Ooze, Harvest Golem, and  Haunted Creeper serve as your substrate for Power of the Wild, Savage Roar or Dark Wispers (which, depending on the board can be used either way).  Poison Seeds andSoul of the Forest further ensure their board doesn't get too scary and ensures you have bodies to buff. 

For turn 1 prioritize your higher damage/more minion start with coin -> Murloc Tidehunter being ideal except vs mage or rogue - then you want Echoing Ooze so they will most likely last another turn. Use your power of the wild as a buff rather than minion most of the time, and a good time to use it is just after haunted creeper deathrattle pops.

Use your minions to attack the hero directly, and your stock of minions on the board will soak up extra damage as your enemy throws its fewer, but stronger minions against them. This works in your favor.

This deck is weak against enemies with lots of low cost board clearing AOE spells, and therefore, if you have the board mostly full, keep some minions in hand for use after their clearing spells.  That said, Soul of the Forest can still give you some staying power, and Force of Nature is always in your back pocket. If the game lasts until turn 9, Cenarius beefs up your minions considerably, but you will most often find more benefit with summoning the 2 treants.  Dr Boom also synergizes by providing extra bodies and is an all around solid card. 

Mulligan: You want your 2 mana minions and innervate as top priority. Wrath is good to have as well. Ideally, you want 3-4 minions on the board for a turn 4 soul of the forest, which will keep the enemy occupied for a few turns as you strike them in the face. 

Combos: Since your minions have mainly low costs and your opponents will have more costly minions,  Poison Seeds works to your advantage any time you have a minion number advantage. Suicide your haunted creepers to get the extra body, suicide your harvest golem to remove one of their minions and hit that poison seed to turn your bonus minions from 2/2 to 2/1 and destroy their threats in the process. If you have been able to cast soul of the forest beforehand, you will double your minions count.

Finishing with "the combo" of Force of Nature and Savage Roar for a total of 14 damage. However, don't be afraid to use Savage roar alone to gain huge advantages when your board is full of 3-4 minions (or less if you need to pull ahead in the early game).