What is a Well Balanced Deck?
RWBY: Amity Arena Guide
A well balanced deck means the synergy of your draws within the battle itself is seamless and that you can relatively defend and attack without any hitch. It might seem easy to pull off at first, but once you've tried your deck on a real battle with live competitor, you'll see that every second counts in playing the game. The moment that your opponent overwhelms your fighters in the battlefield, you'll almost set to lose the battle.
Among the things to consider when building a deck are the following:
1. The variety of skilled Characters to put in, and picking which skills are attuned to your play-style. Different rare and epic cards have different skills that can change the play-style of your deck. It depends on how comfortable you are with the flow of play when in actual battle. That is the reason the game provided a sparring option when building your deck - to test out the synergy of the characters. The main things to consider are putting Main Attackers, Main Defenders, and Decoys (both for holding off an attack, or to misdirect the fighters of your opponent).
2. Balance - consider the number of heavy Characters (tank but expensive to cast), support (volume units), and skilled characters. Usually, heavy characters are used to hold off an attack -- acting like a tank. Their downside is that they usually have the highest casting cost. Skilled characters are used to perform their pertaining skill to create an opening to your advantage (like for instance using Nora's skill of sending away fighters from the battlefield when your opponent puts his/her ace card into play). Common Cards with high unit volume are usually good at holding off a tank until a heavy damage dealer comes to play. Ranged common characters are also used to heighten your attack rate when defending a turret.
3. Combo Cards - there are a number of great combos (pairing a set of Characters in a deck) to put together in your deck -- that being able to successfully cast them side by side would usually give you an advantage.
4. The Average Casting Requirement of your entire Deck - it would make no sense to put together a team of heavy Characters that you'll have difficulty in summoning as it would give you a problem with crowd control. Similarly, putting together a deck of entirely support characters wouldn't get you anywhere in destroying any of your opponent's towers.
Apart from this, there is also the upgrading/leveling part of the game -- where you can typically improve the base stats of the character you are upgrading. To do this, you basically are required to collect a number of copies of a pertaining card you wish to upgrade, along with an increasing value of Lien (as you progress through the levels of that card) to actually perform the upgrade. Of course, to get your hands to those requirements, you'd have to participate and win matches -- in order to earn them through the rewards you get from winning.
Additionally, as you improve on your deck and the very Characters themselves, you'd eventually level up as a player and improve on your rank. What this does in return will improve the base stats of your turrets in the battlefield (both attack and hit points).