Generally the Warlock is played in one of two ways. You will come across an awful lot of Rush Murlock Warlocks in the ladder. This doesn't require a lot of strategy (you just draw and summon en mass) and it is not expensive to play. There is also the Deck Control which is more expensive, based on Golems!
Shadowflame is a powerful spell capable of flattening the enemy table. In the ideal situation you can attack the enemy hero then use Shadowflame, you'll deal damage equivalent to the attack of your creature.
This low cost card can be played in the first turn, wherein lies its strength. Of course, it removes three of your health points, but allows you to take a considerable advantage in the early game because it is a big creature.
One of the best spells to destroy a creature. It allows you to destroy a creature without dealing damage, and to heal yourself at the same time.
A very good zone spell that allows you to wipe out the little creatures on the board. A counter to the little rush decks! Careful, this spell deals damage to your hero, which could be critical, but could also allow you to finish off the opponent.
A 1/3 card with a taunt for only one mana point, it's a very cost effective card. This card allows you to play for time in the first turns to place your creatures on the table or even draw.
A spell that could appear weak but which when used well will allow you to kill a creatures with one health point and draw a card from the pack. Try to use it to destroy a creature and not just weaken it.
A spell allowing you to boost a creature considerably during a turn. It has multiple uses such as: finishing your opponent with the help of four extra damage points on your board. This could be a real surprise with a Leeroy (five mana points for ten instant damage).
A spell that might seem weak on paper due to its discard, but which actually works very well as a finisher. You should only use it when extremely necessary or if it's the last card so that you don't discard card for no reason.
A strong creature. It has five health points in turn 4, making it very difficult to kill at this level of the game! It's a very worthwhile creature that can trade very often with one or two beasts. Its four attack points allow it to avoid the Priest's Shadow Word and its 5 health points avoid death from an Argent Commander or a Shadow Bolt!
HearthStone: Top 10 Shaman Cards
HearthStone: Top 5 Worst Free Cards!
Hearthstone Guide: Definition of a Control Deck
Hearthstone Guide: Top 5 One Turn Kill Combos
Hearthstone Guide: Concept of a Combo Deck