What is the most effective guide to constructing a Duel Monsters Deck?

Answer 1

1) Yugioh supports anorexia. Make your deck as thin as possible (40) since it is generally best to have 40 to draw the cards you need. The only exception I know of is Gadget Decks which uses around 45 cards.
2) Have only one theme as it generally works best like that.
3) Card advantage is important. It is best to include cards that give you a 1 card for 1 card trade. Ex: I Fissure your Monster. It is generally not good to include cards that give you a 2 cards for 1 card trade. Ex: I Magic Jammer your spell. You lose 2 cards which is not good. It is very good to put cards that often give you card advantage.
Ex: I Heavy Storm your 2 Face Down cards.
4) Rituals are generally not good since you lose alot of cards to get them out and they are situational.
5) Keep your situational cards to a minimum. Don't put alot of cards in your deck if they often become a Dead draw(Bad draw). Example of cards that often become Dead Draw: Most tribute monsters, Nomi Monsters(Cards that could not be normal summoned or set and comes out in a specific way. There are many exceptions to this though), Rituals, etc.
6) Don't ever fusion through Polymerization. It is situational, you lose alot of cards to get the fusion out, and becomes a dead draw common.
7) Try not to put too many Traps in the deck since Royal Decree and Jinzo are common cards in competitive enviroment.
8) Versitile cards tend to be good.

Thats all I could think of right now. Hope I helped.

Answer 2

Listening to those with experience usually helps. However, there is really no set guide for making a deck, just guidelines.

1) Make your deck 40 cards or at least as close to it as possible
2) Cards that let you draw are usually good.
3) Keep tribute monsters to a minimum.
4) Magic cards are usually better than trap cards.
5) Stick with one theme or idea (like beating the opponent with Exodia OR reducing their lifepoints to zero, but not both)