1. Draw Cards
One of the most important components of a deck can be card drawing. If your opponents out-draw you, they can end up playing 2 cards per turn to your 1 card. Drawing also allows you to get land out faster to cast those extra spells.
2. Individual Creature Destruction / Removal
You want to make sure that you can take out enemy creatures without taking out your own.
3. Anti Artifact-Enchantment
So many players forget this vital component. Return to Dust is a very nice white mana card for artifact removal. You don't want to be caught with an indestructible permanent on your opponents side. Bounce and theft also will work.
4. Mass Creature Destruction / Removal
You should have some of these cards in your deck. Around turn 6, typically one side has a bunch of creatures out and the other team doesn't. You want to make sure you can handle a bunch of creatures with 1 card.
Along the same lines, you should be able to handle many 2/2 creatures. Hideous Laughter or Infest work nicely. Righteous Cause is a really nice card for life gain.
6. Win Condition
Choose your path and stick to it. A deck divided will fall.
If you are playing cards that take your life down, make sure to have cards that gain that life back.
8. Life Reversal
Sometimes your opponents life will get away from you. Make sure to have at least 1 card in deck to reverse life.
ConclusionKnowing that you have a deck that can handle any situation makes the game enjoyable, especially when you top-deck the card you need. Make some well balanced decks, because you never know what your partner may not have. Then when the situation looks bad, you can say "I have this card in deck, we still have a chance!"
- Good Luck. You'll need it with that terrible shuffler :)