Recommended Reading

This isn't really homework, and to some people the things in this page might seem basic, but everyone should read this before asking questions, because odds are there will be a lot of answers here.

The Really Important Basics
Realm

You picked one of 3 realms at the start of the game. Your goal when building decks should be to get cards that match your realm.

Rarity

There are currently 7tiers - Normal, High Normal, Rare, High Rare, S Rare, SS Rare, Legend, and X Legend. When a card is fully evolved, its rarity advances one step - ie Rare to High Rare. As one might expect, as rarity gets higher, cards get better. Generally when building you start out with lower tier (Rares and High Rares) and gradually replace them with S and SS Rares.

Attack, Defense and Stamina Power
 * Once you've reached a high level, you usually 3 attacks per bar
 * Your defense power needs to be high enough to use your defense deck, with enough extra points to take several attacks in succession
 * Don't go overboard on stamina - sinking extra points into attack will help you more as you grow and your decks cost more to use

Setting up Your Deck

 * Unique cards - with the new update to the game, multiples of the same card become less effective
 * Best skills first - the closer to the center of the deck (first card entered in the edit deck screen) a card is, the higher the likelihood its skill will activate, so put your best boosts or cuts first
 * Bigger is not always better - sometimes just because a skill says "great" doesn't mean it is.  A more specific boost, such as Claymore Maid's "Big boost to man attack," will give better results than a less specific one, such as Dark Knight Luciella's "Great hit to atk/def all"
 * A usual setup consists of three cards with strong skills, followed by 2 cards with skills that might be less useful, but attack or defense stats that are strong

Enhancing and Skill Leveling

 * Always fully enhance your cards before evolving them together!  This can't be stressed enough.  When you enhance cards, their stats improve, and that improvement carries over to the final evolved form.  A bad Hild, for example, has roughly 12.5k attack, while a well-made one has roughly 14.2k attack.  The higher your rarity, the bigger the difference you'll see.
 * Feeders - the cards you use to enhance with
 * It's your choice whether or not to evolve your normal feeders or not - using 4 normals tends to give slightly more enhancement, but will cost more rupies
 * Skill leveling
 * Particularly important once you reach the High Rare to S Rare tier, skill levels improve a card's boost or cut
 * In order to skill enhance, use cards, such as high normals, which also have skills (think Amazon or Dancer)
 * When skill enhancing, the game will tell you the percentage chance of raising the skill level by one before you confirm the enhancement.  As a general rule it's good to have a 60% chance, but it's sometimes more economical to go with less, especially in S Rare cards.
 * Skill levels will only go up by 1 per enhancement - if you have more than a 100% chance, you're using too many cards; save them for the next level
 * The higher the rarity of the card you are enhancing with and the higher its skill level, the better the odds are that it will raise a skill level in another card
 * Skill leveling can be frustrating, but it's advisable to do it yourself or buy a card on the bazaar that's already skilled - people who offer skill leveling services may be thieves and shouldn't be trusted unless they offer you proper collatoral