Variance is the enemy of every deckbuilder.  Most 60 card Constructed decks attempt to be as consistent as possible by running 4 copies of each of their most important cards, but in a 99 card singleton format like EDH, we have to get a bit more creative in order to have any kind of consistency.  There are two ways that we can address the problem of variance in EDH.  The first is redundancy: while you can only run one [card]Skyshroud Claim[/card] in your deck, there’s nothing stopping you from adding [card]Hunting Wilds[/card], [card]Cultivate[/card], [card]Kodama’s Reach[/card], and [card]Explosive Vegetation[/card] as well.  The other way to reduce variance is by including a suite of cards in your deck that can find other cards – in Magic parlance, tutors.

Tutors come in a variety of different shapes and sizes, but with a few exceptions they’re all generally classifiable into three categories based on where they put the cards they find: into play, into your hand, or top of the library.

Top of the library tutors tend to be the weakest at first glance – after all, you’re essentially losing a card and paying some mana to ensure the next card you draw is the one you want.  They tend to make up for it with their speed and extremely cheap cost – leaving a single mana up for a [card]Mystical Tutor[/card] at the end of your opponent’s turn to find exactly the spell you need is not a particularly hard burden to bear for a great deal of flexibility in return.  As long as you don’t need the card you’re looking for right away, that is.  [card]Vampiric Tutor[/card] is nice and all, but it won’t help you when you really need to have that sweeper right now.

Given that these cards inherently suffer from card disadvantage, they’re usually best employed to find cards that net you a great deal of card advantage.  For instance, the classic turn one [card]Enlightened Tutor[/card] to find a [card]Sensei’s Divining Top[/card] can vastly improve your card selection and help you hit every single one of your land drops, or a [card]Worldly Tutor[/card] to set up a [card]Primeval Titan[/card] can let a green deck absolutely explode in the midgame.  Tutoring to the top can also be extremely useful in a few corner cases, like when you have [card]Lurking Predators[/card] on the battlefield, or when you’re playing [card]Momir Vig, Simic Visionary[/card] or [card]Mayael, the Anima[/card] as your general.

Classical tutor-into-hand effects like [card]Diabolic Tutor[/card], [card]Fabricate[/card], and [card]Merchant Scroll[/card] are by far the most common.  They offer the advantage of letting you immediately cast the card you find, essentially appending the tutor’s cost to the cost of the tutored card.  This is the ideal type of tutor for reactive plays, like finding and casting [card]Damnation[/card] after your opponent kicks [card]Wolfbriar Elemental[/card] twenty-three times.  It’s still fine for proactive plays, but unless you have enough mana to find and cast the spell you’re looking for, you have the disadvantage of telegraphing your play, and letting your opponents know something worth countering is coming from you next turn.  If you have the luxury of choosing between a number of different tutor effects, make sure that your into-hand tutors can find your sweepers, artifact, and if possible, graveyard hate.  Furthermore, when playing, don’t succumb to the temptation of casting a tutor right away.  Sometimes it’s best to just keep it in your hand as a wild card as insurance for that time when you really need it.  And believe me, when your opponent casts [card]Genesis Wave[/card] for 20, there’s nothing like being able to find your [card]Planar Cleansing[/card] and cut them back down to size.

Putting cards directly into play is definitely the most powerful of the three options, but aside from some [card Tinker]ridiculously[/card] [card Arcum Dagsson]broken[/card] [card Natural Order]cards[/card], you tend to pay dearly for the effect.  Given that into-play effects fetch permanents of one kind or another, they’re best cast proactively, in order to build up your own board presence or get combo pieces on the table.  For green decks, your [card]Chord of Calling[/card], [card]Green Sun’s Zenith[/card], [card]Tooth and Nail[/card], or other spell is almost always going to be finding a [card]Primeval Titan[/card], although a well-timed [card]Acidic Slime[/card] or [card]Terastodon[/card] can help get rid of problem lands, artifacts, and enchantments once you’ve got your Titan dumping lands onto the table.  Blue decks will usually search up a ridiculously powerful artifact like [card]Blightsteel Colossus[/card] or [card]Mindslaver[/card], and white decks will typically find powerful enchantments with [card]Academy Rector[/card].  Bant-colored or 5-color decks also have access to the most flexible into-play tutor in the game, [card]Wargate[/card].  While it can technically find [card]Ulamog, the Infinite Gyre[/card] for the low, low cost of 14 mana, [card]Wargate[/card] is at its best when it finds 1, 2, or 3 CMC permanents, or even powerful lands.

Of special note among tutors are ones that are attached to creatures, like [card]Treasure Mage[/card].  Not only do these give you a body that can attack and block in addition to finding you what you need, they can also be easily reused by flickering them with [card]Momentary Blink[/card], bouncing them back to your hand to recast with [card]Crystal Shard[/card] or [card]Cloudstone Curio[/card], or sacrificing them and then reanimating them back into play with spells like [card]Victimize[/card] or [card]Reveillark[/card].

All that being said, you don’t want to go overboard on tutors.  While they increase the consistency and flexibility of your deck, they also make it less efficient.  After all, having exactly the card you need at any particular moment is great, but paying an average of 1 or 2 mana extra for each spell you cast can add up in a hurry.  Exactly how many tutors you include in your deck depends a lot on what the deck is built to do, the colors you have access to, and your personal playstyle.  A controlling blue-black deck will probably run far more tutors than a red-white aggro build.

Just to provide an example, my [card]Jenara, Asura of War[/card] ramp/control deck runs the following tutors (not counting fetchlands and ramp spells): [card]Enlightened Tutor[/card], [card]Mystical Tutor[/card], [card]Trinket Mage[/card], [card]Fierce Empath[/card], [card]Defense of the Heart[/card], [card]Tooth and Nail[/card], [card]Green Sun’s Zenith[/card], [card]Drift of Phantasms[/card], [card]Wild Pair[/card], [card]Sterling Grove[/card], and [card]Wargate[/card].  This tutor suite is heavily biased towards getting creatures into play, which meshes well with the overall game plan of bouncing creatures with enters-the-battlefield effects to disrupt opponents and grind out progressive card advantage.  Close examination of the tutor suite will reveal a weakness of the deck, though – it lacks a way to reliably find a sweeper like [card]Day of Judgment[/card].  The deck is built to compensate for this by out-ramping the competition and disrupting opponents’ key permanents, but the fact remains that it has very few answers to a swarm of tokens once they’ve hit the board.  No deck is perfect, though…especially not one that other people will want to play against.