A lot of players, especially newer ones, place excessive emphasis on the power level of single cards. What these players fail to understand is that internal synergy is as important a consideration as single card power during deck building and playing.
Internal synergy is defined as the way the cards in your deck interact with one another. An example of good internal synergy would be playing
Pernicious Deed with very few permanents of your own, or with creatures that regenerate. Poor internal synergy would be like playing
Pyroclasm in a Goblin deck (since most goblins will simply die to a cast pyroclasm, many decks use this card against Goblin decks). When internal synergy is high, decks filled with mediocre cards can become true powerhouses.
I seem to love using this deck as an example, but here it is again: Blue/Green Madness. We all know that
Wild Mongrel is a powerful card. But placing him in a green aggro deck does not make good use of his potential. Even worse would be playing
Aquamoeba in a deck that can't properly utilize his ability's cost (discarding a card). However, when these discard outlets are placed in the same deck as cards with madness or flashback, like
Basking Rootwalla and
Roar of the Wurm, the power level of each card involved is greatly increased.
When I first began playing the game, this philosophy of "synergy over raw power" completely eluded me. My decks were a jumble of what I deemed powerful cards, which didn't build off of one another at all. I was lucky in that my cards didn't get in each others' way (thus resulting in poor synergy), but it still wasn't pretty. One aspect of internal synergy that I completely butchered was the concept of a mana curve. Mana curves are very complex and important things that I won't get too much into now, except to examine how they relate to synergy.
My deck had zero (that's right, zero) one-mana spells. In contrast, it had an overabundance of two-mana and three-mana spells. One of the two-mana spells was
Vine Trellis. Now, to improve my internal synergy I just needed to make a simple alteration to my mana curve. By replacing vine trellis with
Llanowar Elves I would have some first-turn plays (thus using that free mana on my first turn) and would be able to use the elves' ability to accelerate my mana up to three on turn two. This would be great for all of my three-mana spells. Vine trellis, by contrast, took up my second turn and usually ended up giving me four mana on turn three...when I usually only needed three (and it's not like I had one-mana spells to use that extra land). Had I made that change to my mana curve (hint: I never did) my deck would have been better capable of building off of itself.
The next deck I built (again, sorry to be redundant in my examples) was Burning Bridges, which began to touch upon the basics of synergy. My burn spells were cheap, so I could get rid of them quickly, and I never needed to attack with creatures to win, so ensnaring bridge became a three-mana [card]worship in most cases. My deck after that? Yup, that would be Madness (nice trend, huh?).