Magic: The Gathering Strategy
Card advantage is one of the central principles in building a successful deck. (another is time advantage) Improving and maximizing your card advantage, while trying to prevent your opponent from doing the same, is necessary if you plan on moving past just playing occasional, friendly games.
So, what exactly is card advantage?
Simply, it's being able to draw more, and/or better, cards than your opponent. There are two types of card advantage, quantity advantage, and quality advantage. We'll discuss each seperately.
Quantity advantage is just simply out-drawing your opponent. As the game is played by playing cards from your hand, having more to choose from in the first place increases your chance of drawing your better cards, and just plain allows you to play more cards.
This kind of advantage can be created either by spells and effects that cause you to draw more cards, or less commonly, by preventing your opponent from drawing, or foring her to discard when she does draw.
It can also be applied to cards in play. Just about any time you send more cards to your opponent's graveyard than are sent to yours, you've gained card advantage. This occurs because your opponent uses up a card from their hand when putting it into play. This is one reason that enchantments placed upon your own permanents often do not make the tournament cut - because an enchantment upon a creature, for example, allows your opponent to play one creature removal spell, such as Swords to Plowshares, and remove two of yours at the same time.
Now, playing a permanent doesn't always follow this rule. There are some cards which create drawing effects, whether from the library, or from the graveyard. These cards can often upset the traditional card advantage rules - if your opponent plays an enchantment on a creature which allows her to immediately draw another card, and you then eliminate the creature, have you gained card advantage? (Yes, not as much, but still some - and your opponent playing that spell might have given you time advantage in the process).
A large enough amount of card advantage can be a game winner. The famed blue spell, Ancestral Recall, is perhaps the biggest example of card advantage. For only one blue mana, one gets to draw three cards. This is a net gain of two cards, and the mana cost is often negligable - expecially done at the end of your opponent's turn.
Card advantage-producing spells and effects have been toned down since then, and have taken many forms. Often, they cost more mana to play, and even when drawing the same number of cards, usually require you to discard some of those.
Card advantage in quantity is so strong that a continuous method of out-drawing your opponent almost always means you're going to win the game. For example, playing a Howling Mine, and making sure it's always tapped on your opponent's turn, is huge - you are now outdrawing your oppoent 2 to 1, an advantage that quickly yields results.
Any card that can yield card advantage of any significant amount will become the focus of a deck at some point. For example, Necropotence in Ice Age, may have turned off some people at first view. You are giving up your draw every turn, and have to pay life to draw a card - and then, you only get it at the end of your turn. The key is that 1 life per card is not that expensive - especially when you can draw 5, 6, 7 cards at once - enough to hurt your opponent more than you hurt yourself.
Putting your opponent at a card quantity disadvantage usually comes in the form of discard effects. By making your opponent discard more cards than you played to cause that discard yields card advantage - and even an equal number can be beneficial, if you designed your deck to be prepared. Mind Twist, an older black card, was restricted, then eventually banned because it was an X effect, allowing you to make your opponent discard as many cards as you had mana - when you can force the discard of five cards to your one, that's a lot of advantage.
Quality advantage is by being able to get the better cards from your deck, or being able to get a hold of a card you need for a situation when you need it. While every card you put into your deck should be as a good and as versatile as you can make it, you can't possibly predict what you'll be playing against, often leaving you with either suboptimal cards, or even worse, useless cards. Being able to influence what kind of card to put into your hand can be a big advantage.
The most obvious kind of quality advantage involves cards that let you go get a card of your choice - the tutors. Demonic Tutor is the premium example on this principle, allowing you to search your deck for any one card of your choice. Regrowth offers a similar effect, only from your graveyard. It's not just a coincidence that these cards are restricted in Type I play, and were removed from the basic set a while back. Even a weakened version of Demonic Tutor, Demonic Consultation, was found to be too powerful. It also let a player find the exact card they wanted, only they had to flip over cards and remove them from the game until they found it. A serious disadvantage, but it was still too strong.
There have been a number of cards offering the ability to look at a few cards, pick the one you want, and do something with the rest. Impulse let you look at the next four, keep one, and put the rest on the bottom of your deck. Brainstorm let you pick one of the next three cards to put into your hand. Both prevented any card disadvantage by replacing themselves with higher quality, though at a minor time disadvantage. But the quality improvement often makes these cards staples in a deck with the correct colors.
Manipulating drawing can also yield quality advantage. For example, Sylvan Library essentially allows you to pick one of the next three cards to put into your hand. You can pay 4 life to keep a second card when need be, creating quantity advantage also, but the quality improvement is noticable. Especially when a reshuffle effect allows you to look at three new cards every turn, picking the best one.
You can create card advantage in quality by decreasing your opponent's quality instead of improving yours. Being able to remove their better cards before they get to them leaves their deck weaker, less able to respond to your threats. For example, Lobotomy allows you to look in their hand, pick a card, and remove all copies of it from the game. If you hit one of their better cards, it guarantees they won't draw it, drawing preferrably less effective spells instead. The artifact Jester's Cap lets you pull any three cards out of their deck - if you understand what they're playing, this can quickly hamper their quality.
Combining the Two
Sometimes, you'll find an effect that will in some way combine advantage in both quality and quantity. These usually will have limited effect in each way, usually very, very minor - and are still strong.
One great example is Thawing Glaciers. It allows you to slowly pull land out of your deck, and put it into play, returning to your hand. It's like a free draw of a land card. Now, normally drawing an extra card every turn, but only if it's a land, may not seem like that good of a dead. But when you remember that your deck is likely to be at least 1/3rd land (to give yourself to proper chance at drawing land at the beginning of the game), you'll be drawing one every third turn. By pulling it out in this way, you've decreased your chance of drawing a land card for your normal draw - and thus increased your card quality. The fact that your mana available increases is a nice secondary benefit. (Now, if we have a draw helper like Sylvan Library, the reshuffle effect from the glaciers really improves quality, by giving you a new selection after using the glaciers.)