Ok, so I have decided to do a quick guide, so here it is.
When building a deck, you need to have a theme. Without a theme, you are, no doubt, going to have a pointless, dead-drawing deck.
If you left the game when it was in its early days and you have only just returned, there are no longer cookie cutter decks. What I mean by this is there are no decks in which you can throw the best cards around, into it and it will work.
With so many deck types around and more always coming out, it is hard to stick to one type of deck; I personally have multiple decks on the go at one time, using them depending on the surrounding and my feelings.
If you are unsure of what deck you want to play, then one of the best things you can do is use a site called ‘Dueling Network’. This site is an online database in which it has every card in the game and is always updated. You can create a deck and play other people, random or friends and test out decks. This is one of the best tools around for a duelist; not only do you get to know your combos and how the deck works, you get use to how others duel against you and what counters your deck.
In the game of Yugioh, there are cards in which are called ‘staples’. This simply means that these cards should be in EVERY SINGLE DECK THAT IS BUILT. They include cards, such as:
Post September 2011 Banlist
Tour Guide of the Underworld
Mystical Space Typhoon
Black Rose Dragon
Brionac, Dragon of the Ice Barrier
Trishula, Dragon of the Ice Barrier
Ally of justice Catastor
These cards are the basic monster and back row killing cards that should be put into the deck, if not having some serious consideration.
What types of decks are there?
There are many decks in the Yugioh world, but it boils down to Meta and Anti-Meta.
Meta: Meta Refers to the Deck(s) in current competitive use that are having the greatest succession in the professional play scene.
Anti-meta: An Anti-meta deck is any deck that is built to counteract the most popular decks being played.
That is it put in a nutshell. In a tournament, you will normally find 80%-90% of people running meta and the rest Anti-Meta. Why don’t more people run Anti, I hear you ask. Because they aren’t consistent enough. A good yugioh player will take into account their meta decks weaknesses and in the second round of duelling where siding is allowed, they will cover that weakness and render the deck helpless.
What to avoid?
There is nothing stopping you making any deck that your heart desires. If you want to build that Batteryman OTK then go for it, but if you want to play in local tournaments or bigger events, then you are going to need to go with the popular, because it is popular for a reason.
Getting the balance of a deck is the most important thing. You can’t just throw in all monsters, spells or traps, obviously there are exceptions, but only one or two decks at the most fall into this category. (Monster mash or Fuma FTK/OTK)
What is the most important aspect?
TEST TEST TEST!
You HAVE to test your deck in any way you can. Don’t want to go on DN? That is fine, use real life friends. Don’t have any around? Just use the deck against you. One way I test is by shuffling and playing as if someone was in front of me, guessing what will most likely happen, but this does take time to get right and you have to be very clued up on the meta to be able to do this. Just draw 5 then one for your turn and see what combos you can get going. If you have gone more than 2-3 attempts and not been able to pull off the deck/s combo, then you need to think about your deck and go back to the drawing board.
What should I know?
The main things that you need to know are the popular cards in the game today. If you know, you are blind-sighted in what combos will come your way and you have no hope in countering them.
Guess what your opponent is going to do, get inside their head, what would you do if you were them?
If your opponent doesn’t do anything on their first turn, it is very likely they have Gorz or Tragoedia in their hand, so work around it, build up your defence or have a strategy if you are going to attack.
Don’t be reckless, if you are reckless, you have already lost. The amount of times I have seen someone lose and beat someone because they get so excited that they are going to win, they miss the obvious counters that are there.
I can’t afford a big build, what do I do?
Yugioh is very expensive, everyone playing knows this. Your extra deck will cost you £100/$150 alone if you want the staple cards. So what are the expensive and cheap decks, but can hold their own? (Will be updated)
OTK/FTK decks (Meaning One Turn Kill/First Turn Kill)
Yugioh is a game you have to spend time and money on if you want to play it as it should be. If you want to enjoy but don’t want to spend money, stick to Dueling Network and the console games.
It is a game at the end of the day that it is fun. End off. ENJOY!
The fact that one needs to have a theme is not necessarily true; however it is highly suggested that if one does not know what one is doing to play a deck revolving around a certain strategy. Goodstuff.dek still exists, though, and is actually remarkably effective when it is played (though not necessarily as effective as a streamlined singlepurpose deck).
Dueling Network is an excellent website, as Fabio has mentioned.
Staples should /probably/ be in every single deck that is built if you have space and they do not conflict with the core strategy of the deck; as well,you should not able to play cards that outclass them. If any of the above three are untrue, then staples are not in fact must-haves for one's deck (of course, Dark Hole and Monster Reborn are blatantly overpowered, so... make space for that kind of thing).
Tour Guide is not a staple by any sense of the word; it is a powerful card but not every deck needs it. It is highly splashable and very good, which is something entirely different. Effect Veiler would probably be more of a staple than Tour Guide.
Trap Dustshoot is a staple that is missing. Torrential Tribute is still (probably) a staple.
In fact, the only cards I would advocate running in every deck are the trinity of Limited Spell Cards (Storm / Hole / Reborn) and Trap Dustshoot. The other ones are all situational to varying degrees.
Extra Deck staples are fine-ish; depending on the deck's availability of levels a number of Xyz Monsters are also staples - notably Wind-Up Zenmaines, Number 25: Leviathan Dragon, Leviair the Sea Serpent, Number 39: Utopia, Gachi Gachi Gantetsu, and Steelswarm Roach.
Re: Deck Types
Yes. Also streamlining one's build, finding interesting pieces of tech, and crafting a deck that is able to meet almost every challenge with a mode of defense / counterattack. Try playing against the top decks of the format to see how your deck matches up against other decks, and make mental notes of glaring weaknesses to certain deck types.
Re: Things to Avoid
Don't make your deck more than 40 cards, please! It just makes it less consistent and all around worse than if you had only 40 cards. No, it doesn't matter if you want to include another copy of your favourite boss monster or whatever - cut something else if you have to. Single most prevalent and easy-to-fix mistake that is made in playing YuGiOh.
Re: Balance of Cards in One's Deck
I would actually say that everything is situational and as long as you can consistently find a way to win, it doesn't matter that much if the ratios of monsters to spells to traps are a little off (i.e. if you don't kill yourself because you had no monsters for a couple turns and this happens often, edit your deck, but if you run a more monster-intensive or turbo deck then it is acceptable to have varying monster counts - my decks range from 15 monsters to 30 monsters depending on purpose).
Re: Not Doing Anything on Someone's First Turn
This doesn't telegraph that they have Gorz or Tragoedia. : p It /might/ but it doesn't usually. (UNLESS YOUR OPPONENT IS BAD, OF COURSE - IN WHICH CASE THAT IS A DIFFERENT STORY.)
Re: Things One Should Know
Try to understand your opponent's deck; what combos does it have? What cards does it need to win? What can your opponent do to you that you need to watch out for? This knowledge is accumulated by exposure to the game, and so don't worry if you don't get it at first, but it is something that should be kept in mind.
Do not play too aggressively, but do not play too passively either. You need to pressure your opponent if you are letting him simply accumulate advantage every turn by not being forced to expend his resources, and every attack counts in this format (where life points matter again)! Attack with cheap, expendable monsters whenever you can to push for damage. It allows you to move that much closer to victory.
Re: Being Able to Afford Good Decks
YuGiOh is an expensive hobby. I recommend you QQ about Konami's policies of only wanting money (overpriced broken cards and super high rarities, aww yeah) and then play card games on DuelNet. (In all seriousness though the game is actually really expensive; though it's not as bad as POT OF DUALITY SOLEMN WARNING EVERYWHERE YEAH important cards for builds are still expensive.)
Dark World isn't cheap; Tour Guide is staple for them. : (
I would actually say Plant Decks are not that expensive compared to other decks like Rabbit Lagia and Dark Worlds.
OTK / FTK decks ... depends on the build.
Basically the idea here is: find good cards, buy at low prices if applicable to build. Rinse and repeat.
KOWM. (Konami Only Wants Money.) ;_; It is not recommend you buy actually expensive cards as they might / will fall out of fashion after the banlist hits; perennially good and cheap cards are better investments. (Like Gladiator Beasts; they're not likely getting nerfed any time soon).
I don't really have much to add to what's already been said. I will mention that dueling people face to face is far better than dueling over the internet as far as preparation for offline events is concerned. This is because the actual interaction between players is far more in depth when dueling face to face as opposed to online. The body language and psychological aspect of the game is exemplified in real life dueling and that is something a duelist needs to develop to perform well in tournaments. I've gone a bit off topic though lol.
"Power through ambition." - Overlord Drakow Forum Set