There are three types of Magic decks: 40-card decks that you build on the spot, 60-card decks built for power, and 100-card decks built for laughs. We’ll start with the 60-card variety: constructed decks.
Technically, 60 is the minimum. Your deck could have more than 60 cards. In practice, players never include more than 60. Feel free to do whatever is fun for you. The consensus is that you’ll win more with 60 than with 65, 70, or even 61. However, a spirited minority believes that there are sometimes reasons to use 61.
You can have up to 4 copies of each card in your deck. So, if you use 24 land and 36 spells, there could be just 9 different spells in your deck. That’s how easy it is to brew a deck!
The spells in your deck should differ in mana cost. Some should cost one or two mana, and some should cost three or four. Much of the time, you will also include a handful of “bombs” that cost five, six, or more.
If you use 24 land, there’s a good chance that you’ll have 3 in play on your third turn, and 5 in play by your seventh turn. Plentiful mana is so important that most strong decks run this many lands - even though it increases the chance of drawing land late in the game when you’d rather get a spell.
You want your deck to be consistent, so several of the key ingredients will be 4-ofs. For ancillary strategies like protecting your creatures from removal spells, drawing extra cards, or removing non-creature threats, you might include just 2 copies so that you don’t get stuck with them when something else would be more useful. As you balance things out and make guesses about which threats you’ll face, there may be certain cards that you include 3, or just 1, of.
This basic pattern of allocation is why most decks have about 15 different non-land cards (not just 9). You want to build up your own strategy, have answers for the threats you’ll face, and potentially, answers for the answers that your opponents will use to disrupt your scheme.
While you are picking your mix of 15 cards, you’ll be mindful of how many colors are represented. This is because most lands can only produce one or two different colors out of the five. If your deck includes too many colors, it becomes more difficult to cast good spells, especially early in the game. Many games are over by turn 10, so if you’ve cast just two spells by turn 5, that can be pretty bad.
If you have great lands, they make it easier to use multiple colors in your deck. Two colors is a great place to start; many decks use more, and as long as you plan your land accordingly, it’s not a big disadvantage.
At times in the overview, I’ve mentioned that you use 'creatures and spells', but technically creatures are also spells, so they’re included in these numeric breakdowns. In fact, most decks are mostly creatures. Out of the 36 spells, an average number of creatures is about 20.
Creatures play several roles for your deck. The goal is to get your opponent’s life from 20 to 0; creatures can do damage every turn, they’re the most efficient way to do damage. They can also block your opponent’s creatures from damaging you - and a small, cheap creature can block a big one that might otherwise hurt a lot.
Most creatures have rules text that either gives them an ability, changes the state of the game, or preemptively replaces one event with another. The activated or triggered effects go on the stack, and can therefore interact with spells. The state-based effects and replacement effects are not interactive, but players can react to the creature entering the battlefield.
Within a color, you’ll find creatures armed with similar effects. From year to year you see lots of variations on themes. So, you can have multiple creatures with similar abilities; or you might find the best variant for your shell.
Here are some examples of how you might use spells to strengthen your deck. In each game, some of your creatures will die - so you could include spells that can protect or resurrect them. Alternately, you can focus on making the ones that live as strong and evasive as possible. Or, try to disrupt spells your opponents cast.
Certain spells can do all three. Feat of Resistance could win at combat, enable a massive block, counter a removal spell, or remove an aura. How often will your creatures be in those situations? Probability can improve your deck.
To have the best deck, you need to have an idea what you’ll be facing. In each major format, there are dominant strategies at any given time. If you’re mostly playing casually with friends, then you’ll know which cards they like.
Plan for cards that are going to give you trouble. Some decks will destroy your big creatures, some will assault you with huge creatures of their own, and some will eliminate your most powerful cards before you even get to use them. Try to have a back-up plan for each of those types of interference.
You get to bring 15 extra cards to answer these (and other) threats - this is called your sideboard. Magic is played as a best-2-out-of-3 match. After the first game, you swap in cards from your sideboard. If you survive the second game, you can make adjustments again. After the 3-game match, your deck must be returned to its original state before you face your next opponent.