Top Decking is a term I've never heard of until a friend told me about it (thanks Rhyz). Basically, you are hoping for a card to either win the match for you or at least keep you alive one more turn until you draw the card that changes the entire match. I have been on both sides of this while playing the Hearthstone Beta and I wanted to discuss some strategy.
I was playing an opponent and had maybe three low level Spell Cards I could use. My opponent had the Priest hero (which lets him recover two health each turn by paying 2 mana crystals) and he had many low level cards. I decided to try and get rid of his health has quickly as possible and see if I can beat him quickly. He did not play any effective cards until round three or four. During the first two rounds, he played simple minions that I took out with my minion and wasted my spell cards.
I thought I was doing well. I believe I got his HP down to nearly 17 HP or so after two or three rounds, but then I realized I was out of cards sooner than I thought. Basically, I was drawing low level minions and he then had nearly 4 minions on the field out of nowhere. Instead of wasting all of those spell cards in the early rounds, I should have saved them to defeat my opponent. He was not that good and kept on getting lucky. I just kept waiting for a card to change everything, but that never came. I lost to him, but learned a valuable lesson: do not fool yourself with the top of your deck.
The Waiting Game
After losing as I did, I told myself I would not make the same mistake. Later that night, I found myself against an opponent who did exactly what I did before. At first, it did seem like they had the upper hand. I saved a lot of my spell cards and played the waiting game. I believe he had nearly knocked me down to 12 HP and he had 28 HP. Then, he was out of cards. I had a lot of cards that would power up each other. All they kept on doing was using low level starter cards, but since most of them were weak, I could take them out pretty quick. I believe at one point, he had nearly 4 minions and I had two different taunts, and released hell upon them with spell card after spell card. I hope my opponent was freaking out since he might have left early after he knew his doom was eminent.
What To Choose
At the beginning of each round, you are allowed to replace cards. This can be very vital to the start of the match. Basically, if you draw lots of high level cards like in the picture above, it may take a long time until you can actually use them. What I recommend is either getting rid of them all, or the ones you can live without until you draw them later. In this case above, I would most likely take a risk and keep the Taunt and Battlecry card since you are expecting three more new cards (hopefully one will be something reasonable that is needed in the beginning of the match).
Also, the Coin card or cards that give you more Mana crystals are VERY important. Use them wisely. They can get you out of tight spots and can be saved until later in the match when you really need one. I believe I've waited until nearly the 4th round to use one to place a level 5 card down.
As you can see, there is a lot of strategy to this game. I thought I would give my thoughts on this game since no one has talked about it on here.
I hope you enjoy!