This will be a guide for beginners that are interested on getting better, and get started on the competitive play of Yu-Gi-Oh. Keep on mind that not everything on this guide may apply to every deck, on every format, because this is a game that changes a lot every format, and every deck have their own way to be run.

-Deck Building-

Concistency:
Concistency is aways something important, you don't want to have a lot of dead draws, and also you wanna draw your combo pieces as fast as possible, so many things are applied on this category such as:

• Deck Count: Most times, having a 40 cards deck is better, since if you have 40 cards on your deck, at the moment you draw one card, you have 1/40 chance of this card being a specific card, but if you have 60, you will have 1/60. Keep on mind that is not good to try to bet on luck to win, so having a thin deck with few cards that could be a dead draw, you have better chances.
  
  
• Deck Thinning: Anything that makes your deck most accessible, for example Upstart Goblin, if you have three upstart goblin you potentially have 1/37 chance to draw what you need, because even if you draw upstart goblin, you can use it to draw another card.
  
  
• Searchers: Probally what counts most when it comes to concistency, because if you have a card that can search for multiple card in your deck, you have options, for example Tenki, as you can search for any Beast-Warrior monster, you can pick the one that fits better the situation, also this is another way of making your deck even Thinner, just try to avoid running more searchers than targets for the searchers.
  
  
• Avoiding Dead Draws: Sometimes you gotta ask yourself "This card really worth a spot here?", for example, if you have a deck that is based on light monsters, and you run two tragoedia, is this really worth to put in a Black Luster Soldier or a Chaos Sorcerer? Those cards could be potentially dead on your hand most of the times, so picking the right cards is aways important.
  

Sophistication:

• Replacing Cards: The same as above, but this time, you gotta look if it is really worthy not because of it being a dead draw, but to see if there is a card that makes the job of this card better, because you have limited space on your deck, and you probally don't wanna have more than 40~45 cards on your deck, so you have to check if the card is really worth to be run, and if there is no other better replacement for it.
  
  
• Staples: Staple cards are cards that just have a effect that is too good, Dark Hole, Monster Reborn and Heavy Storm, most of the decks can run those cards, but however, it's not a law that you aways have to run these cards, if you have a deck with a lot of Continuous traps/spells, you probally won't want to run Heavy Storm, and on most high tier duels, Dark Hole could be not that good, since Dark Hole is a heavy punishment for Over-Extending, wich competitive players won't do.
  
  
• Techs: Just cards that can be way too good with your deck, or that can put another deck in a bad situation without hurting your deck, most of the cards to counter another decks are going to be put on the side deck however, because they only work for specific decks, and you don't want they doing nothing in a mirror match for example. On the actual format (March 2013) a lot of card that were before on every deck, are not moving to the side, for example, Mystical Space Typhoon, since all you can do with it agains't deck like Spellbooks, Elemental Dragons and Mermails is trying to blind hit one of their backrow (if they even put backrow in the case of the elemental dragons) and hope it's something, but most of the times it will be chainable, and you basically just wasted one card on your hand for nothing, so keep on mind that techs change a lot from format to format.
  
  
• Don't rely on luck cards: Cards like Cup of Ace, that can give you a good boost if you got lucky, is not exactly good at all, the less you can bet on luck, the better your deck will score.(Unless you're very very lucky)
  

Side Deck:

It's most of the times, what decides wich player will win and wich player will lose on a competitive play, because some cards can put certain deck in a very bad situation, and other cards can save you from a very bad situation, so siding works for both, taking advantage of their weakness, or removing your opponent's advantage over your deck.

You also have to know what you wanna counter, I'd say on this format, thinking on the metagame (online - TCG/OCG March 2013), you would probally try to make your deck based around Elemental Dragons, Spellbooks and Evilswarms, however countering things like Mermails and Fire Fists is something to keep on mind if they can hurt your deck.

If you have something you would like to add, or something you don't agree, feel free to leave a comment.