The Art of Making a Deck

Let's start with some simple rules:
1. Anyone can make a deck.
2. Don't throw cards in a pile and call it a deck.
3. Prepare for your metagame.
4. Test, test, test!

To make a rogue deck, you must start with an idea. Let's brainstorm: Megrim, Phytostomp, Zuberas. Mind you, these are only a few ideas, but I will go over how to make a rogue deck well.

Section 1
Card choices
Obviously, to make a deck, you need to choose cards to put in on it. Let's do the Megrim deck. What cards are obvious staples? Megrim? Duh. Hypnotic Specter? Obviously. Ravenous Rats? More than likely. Alright, that was easy. It gets harder. When selecting cards you need to think about a lot of things: Does this card have synergy with my deck? What can this card do? Is there a better card to use? Megrim: Lots of synergy, it deals damage when a player discards a card, there is no better card in a Megrim deck. Hypnotic Specter: Tons of synergy, it deals damage and forces a discard, this is a staple in my deck. Ravenous Rats: Plenty of synergy, has a 1/1 body and forces a discard, there may be better cards.
How do I know if a card is good enough for my deck?
Consider this: Abilities, Cost, Synergy, and Power. Cards with low costs that have great abilities and power are generally staples in every deck. You obviously want cards to have synergy with the rest of your deck. I am not saying that you don't want high-cost cards in your deck. But for a higher cost, expect a much better ability and power. Let's take a look at the only questionable card in the deck so far: Ravenous Rats.
Abilities: Forces a discard, and chump blocker.
Cost: 2, which is relatively low for what I'm getting.
Synergy: My deck wants to force discards, so yes.
Power: Moderate, it is relatively powerful in this deck, but nothing game changing.
So should I add Ravenous Rats? Yes! Its cost to abilities is very important in this deck.
What is synergy, and how do I know if a card has it?
Synergy is a characteristic a card has that means it works together with the other cards in your decks. A card has synergy if it works with the theme of your deck, works well in your deck, and can accomplish something that will help you win the game. Power does not mean synergy. Weakness does not mean a card has no synergy. If you are playing, let's say, black weenie or aggro, you more than likely shouldn't run Kagemaro, First to Suffer. Sure, he's a very powerful card, and can change a game, but he won't work very well with your deck. Not only should you empty your hand very fast, but he'll also ruin your board. It's simply common sense. Some other choices will be a bit harder, so thoroughly think each card in your deck. If you are playing a discard deck, then you should probably run cards like Megrim, Ravenous Rats, and many discard cards. Even though most of these cards are relatively weak, they have great synergy in the deck and will work together. More common sense, but just be careful.

Section 2
Support cards
Next we should cover cards you add that don't necessarily have perfect synergy in your deck, but that support the deck well. In the Megrim deck, you will probably run removal like Last Gasp. Does that card have synergy? No, not really, but it supports the deck. It kills creatures so you can live longer or push attacks through. Tutors are also considered support cards. You should probably run Dimir Machinations. Does that card have synergy with the rest of your deck? No, not really. What it does, though, is it allows you to tutor for several cards in your deck. You can get Hypnotic Specter, Megrim, etc. It also can rig your deck so you draw what needed, or rig your opponent's deck. There is just one important thing to remember: Always make sure that the support cards you use support your deck well, and are good against your metagame, not just random decks.

Section 3
Card amounts and land amounts
Alright, next we should discuss how much of a card and how much land to put in your deck. Let's start with mana fixers and acceleration. Mana acceleration is very important in decks, and any low cost mana fixers and accelerators should probably be 4x. It is very important to get these in the early game, so you want the max amount you can. Any legendary cards, unless VERY important, should be 2-3x. For instance, if you make a Shirei deck, you will probably want 4x of him, unless you run plenty of tutors. That brings us to the next part: Tutors. Tutors should generally be 2-3x. If your deck runs TONS of important cards that are tutorable by such a card, you can run 4x. Support cards depend on what kind of support they provide. Cards like Sensei's Divining Top should be 4x, because of its utility and low cost, wanting it early. Depending on your metagame, removal should be 3-4x. Generally speaking, 4x is optimal for early game removal or versatile removal. Putrefy often finds a 4x home because it takes out creatures, artifacts (Umezawa's Jitte), and it prevents regeneration (Ink-Eyes, Servant of the Oni). Cards like Final Judgment and Wildfire will probably find a 3x home, because they are late game cards.

What about creatures and other threats? Those depend on a couple of things: Importance and Cost. Aside from legends, addressed earlier, low cost threats should be 4x, especially if you really want to draw them early on. Cards like Hypnotic Specter should be 4x, because they are very important, and relatively low cost. If you run Gleancrawler in a beatdown deck, you'll probably want 3x. He is probably something you want something a lot later on just to finish up your opponent, and this takes away from his importance. Plus, he has a relatively high cost.

What about lands? Land amounts can vary from 18-28. I have seen few decks with land amounts 10-15, but they are decks that run many 1 mana accelerators, like in elf decks. This depends on your deck type and your mana curve. Your mana curve simply consists of all the mana costs in your deck and how many of each, starting with the least, ending with the most. In a weenie deck, I highly suggest running 18-20 lands, because you want lots of creatures and few lands. In a non-weenie aggro deck, I suggest 20-23 lands, because you want lands to play creatures, but not too many. In control decks, I suggest running 22-26 lands, because you will want lots of mana to play cards to hold your opponent and to play your big cards. In many colored decks, lands should be near the high end, but that depends. Cards like BoP (Birds of Paradise) and lands that produce more than 1 color can save you from having to run too many lands. Particularly, look at guildlands. Not only do they produce 2 colors of mana, but they also return a land to your hand, which allows you to continually play lands without drawing more. They can reduce your land count 2 or so lands. Next time you make a deck, consider the lowest and highest mana costs in your deck, and how many of each cards you have of that cost, and then add lands. Do this carefully, and usually after you make your deck, changing amounts of cards as needed. If you see most cards around 1-2 cost, run only 18-20, 3 cost, run only 20-22 lands, 5 cost 23-24, 6 cost and on, 25+, again depending on what types of lands you run and what colors you have in your deck.

Section 4
Analyze your metagame and sideboard
The final step in making a deck is realizing what your metagame is. What is metagame? Metagame is the field of decks that your average opponents in your area use. If you plan on going to the worlds, however, plan for major netdecks. Let's go on. If you find MUC is very popular where you play, run anti-blue cards. Isao, Enlightened Bushi is an obvious choice here. Dredge cards are also great against MUC. If you find Aggro is heavy in your area, run removal in your sideboard, such as Wrath of God. If you find weenie is used a lot, use cards like Threads of Disloyalty or Reverence. If you plan for combo decks or decks revolving around a card, run Cranial Extraction. Other generally useful sideboard cards are: Naturalize, Pithing Needle, Seed Spark, Arashi, the Sky Asunder, Pyroclasm, Hearth Kami, Kami of Ancient Law, Faith's Fetters, Terashi's Grasp, Boseiju, Who Shelters All, Ivory Mask, Shadow of Doubt, etc., etc., etc. Just make sure your sideboard isn't what generally is used, but what is good against your metagame.

In summary: Choose cards wisely, properly support your deck, put in card and lands amount as your deck requires, and set your sideboard to your metagame.