ome cards combo very well with other cards. An Arrogant Wurm goes well with a Wild Mongrel, an Illusions of Grandeur goes well with a Donate, a Royal Assassin goes well with a Blinding Mage, etc.
There are countless cards with a unique function that happen to go particularly well with another card that has a distinctly different unique function. But some cards become better when they are surrounded by other copies of themselves and functionally similar cards.
You can see obvious examples of this by looking at creatures that provide a tribal bonus, such as Veteran Armorsmith or Sinew Sliver. The more Soldiers or Slivers you have, the better they will be.
But there are other cards, such as Jackal Familiar, that get better and better when they are surrounded by similar cards. A lot of the time Jackal Familiar will be trash in your deck. If a Jackal Familiar is your only creature that costs less than three, it will border on unplayable.
Jackal Familiar can be very good, however, provided you have a lot of other cheap aggressive creatures and some removal. If you have a stack of Jackal Familiars and Sage Owls, your deck will likely be much better than the sum of its parts might suggest.
Why? Because you are actually allowing your cards to perform at full throttle.
Your competitive goal, whenever you are drafting, is to maximize your ability to win. Sometimes you accomplish this by taking the most abstractly powerful card (a decision that people will often make early in the draft and during their early picks in subsequent packs), but the majority of your picks will be made taking the best card to complement what you have already drafted, as well as what you plan to draft.
Just Because It's OK to Play One ...
... doesn't mean you want to play multiple copies of a card.
Sometimes a card is really good in your deck because it's surrounded by lots of similar cards. But some cards get much weaker when you have multiple copies of them in your deck. For example, your third Drudge Skeletons, or your third Duress, won't be very impressive additions to your deck unless you are playing against a strategy that is extremely dependant on giant ground creatures or huge spells, respectively.
Your first mana fixer, such as a Rampant Growth can be extremely important if you need to support a splash card. You might even take it over a card that you would really want for your deck, such as a Centaur Courser or a Craw Wurm. But if you already have two Terramorphic Expanses, and the acceleration isn't particularly relevant for you, you might take a Runeclaw Bear or a sideboard bound Mold Adder over it because you simply don't need the extra mana fixing.
You might decide that it's okay to play a single Sage Owl in your white-blue deck because you are lacking early drops and you want a way to smooth out your draws, but any subsequent Sage Owls are going to look pretty bad unless you have a couple of Terramorphic Expanses to allow you to shuffle away unwanted goods.
Being Aware of the Undesirability of Multiples
Be aware that even if you got significant value out of the first copy of a card, that doesn't mean that you need or even want more of them. If you feel that a card fits this description, then a lot of the time it will make sense to pass up on the first copy of the card (unless that first copy is extremely vital) early to midway through the draft in the anticipation that you will see more of them.
Entangling Vines is an example of a card that I will take noticeably higher in pack 3 than I will in the first two packs. Most of the time I will be happy to play a copy or in some cases even two copies of Entangling Vines in my deck. But unless I'm really starving for removal spells I won't want to have too many copies of this cumbersome enchantment in my deck.
In the first two packs, I'll pick it up if there isn't anything else appealing to me in the pack. But by pack 3, I'll know exactly how bad I want Entangling Vines, and I won't be concerned with the possibility that I might get too many of them, that I'll take it much higher than I would have anytime earlier.
How to Know if You Want More of a Card
Lava Axe is a prime example of a card that can be either better in multiples or better as a one-of. You might be looking for a finisher in your mid-range red-green deck, and having that one Lava Axe might provide you with just that extra push that you're looking for.
Or it might turn out that you have a low enough curve that you can easily swarm your opponents for 10 or 15 damage, so you want to play as many Lava Axes as you can get your hand on to allow you to actually kill your opponents before (or in some cases even after) they've gotten a chance to take over the game with their more expensive (and bigger) spells and creatures.
But how do you know early in the draft which way your deck is going to go? You have two options. You can go for a more passive strategy, wherein you take a safe pick like a Canyon Minotaur over the Lava Axe. Or you can look to take a stand and draft a synergistic deck wherein your Lava Axe(s) will be a key player.
There's rarely a single right answer to these types of questions. You just have to understand why you are making the decision that you are making.
Some cards really rely on being surrounded by a lot of cards that require similar commitments in order to reach their full potential.
Fireball doesn't necessarily go up in value just because it's surrounded by other Fireballs (though it's far from a bad thing to have multiple Fireballs). It's always going to be awesome, because it's always going to be a Fireball. You might be playing mono-red, or you might be playing a white-blue deck with a Mountain and a Terramorphic Expanse as your only way to support your spell. It's going to contribute to a lot of wins either way.
The same can't be said for cards with large color commitments. Tendrils of Corruption and Consume Spirit become noticeably better with each additional copy that you pick up. This is because you gain a larger and larger incentive to play a lot of Swamps. Tendrils of Corruption is going to be good even if you have as few as 7 or 8 Swamps. But Consume Spirit doesn't become interesting until you have 9 or 10 black sources, minimum.
You often give up a good amount of opportunity when you decide to draft a monocolored or nearly monocolored deck. You hope to regain that value through increased consistency and the ability to maximize the value of some of your cards.
While it's extremely rare to get three Fireballs in a deck, it's not at all unreasonable to see someone with two Tendrils of Corruptions and two Consume Spirits in a deck with 18 Swamps. Nobody else nearby could put the cards to good use, so the person who could put them to the best use got 'em. And now those Consume Spirits are noticeably better than a universally bombtastic Fireball would be.
When you spend early picks on cards like Consume Spirit or Vampire Nocturnus that require huge color commitments, you are then incentivized to take more cards that offer high upside in exchange for a huge commitment.
If things come together, you'll be in great shape.
But if they don't you might find yourself at a serious disadvantage when it comes time to shuffle up your 40 cards, because you jumped ship and wasted a bunch of early picks on speculative cards, or because you were forced to fill your deck out with a lot of undesirable Gray Ogres in order to have enough playable cards.
The Best (Available) Card for the Job
In Constructed, people will frequently play cards that are inferior to another card in their deck so that their deck can reliably function the way that they want it to.
In Extended, a mono-red burn deck might play a full set of four Incinerates to go with four Lightning Bolts, a green-blue Madness deck might shuffle up four Aquamoebas even though its pilot would prefer to draw a Wild Mongrel 98% of the time, or a red-green-white Zoo deck might have some Isamaru, Hound of Kondas to go with its vastly superior Kird Apes and extremely powerful Wild Nacatls.
The same thing goes on in Limited.
You might really want a Terramorphic Expanse to fix your mana, or you might really want a Seaside Citadel, but you may have to settle for Rampant Growth or a landcycler to help you cast your splash. And, when the third pack rolls around and you still haven't picked up any way to support your splash, you might have to take that mana fixer very highly even though it's not the mana fixer that you want.
You might be drafting a hyper aggressive blue-red deck filled with Jackal Familiars, where you really want to pick up some Zephyr Sprites, but you might have to play some Sage Owls to complement your one-mana fliers.
You might want to pick up a Naturalize type card for your sideboard, but the only thing you can find is a Shatter. Or you might really want some high-quality removal spells (after all, who doesn't?), but instead you might find yourself needing to pick up a Weakness with one of your first few picks in pack 3 because you simply don't have enough ways to deal with creatures.
As a drafter, one of the most important things you can do to maximize your chances of getting a very good deck is to remain vigilantly aware of what you've already drafted and what types of cards you would like to draft to complement them. This is relatively easy to do in the first and third pack, but it can be quite difficult to do when you are in the middle of the draft.
If you never take a stand, always taking the average Canyon Minotaurs over cards that might allow you to work towards a concise strategy such as Lava Axe, then your decks aren't going to have nearly as much potential as they should. No, that type of pick won't really lower your chances of having a fantastic deck by much, but without taking a stand at some point you're going to end up with a lot more mediocre decks than you have to. But it can be quite dangerous to make a stand too early, because those first- and second-pick Consume Spirits might put you into a very undesirable spot if it turns out that the neighbor to your right is in black.
Early on in a draft it will often make sense to play it safe, taking relatively unspectacular picks while you get a sense of what is going on at your table. But at a certain point—maybe it'll be fourth pick, maybe it'll be eighteenth pick—you're going to have to figure out what types of cards you want to maximize. And once you do make that decision, don't be afraid to stick with it.
After all, one Jackal Familiar might be unplayable, but once you have five they become pretty great.