The central tower is defended by two side turrets which will attack nearby enemies automatically. The central tower will not activate unless it is attacked or one of its side turrets fall. Therefore the best strategy is to focus on one of the side turrets first.
Balance your Deck
It is important that you have a balance between cheap and efficient cards and expensive powerful cards. Your deck of cards also needs to have a balance of cards so you are able to counter several different units from the opponent. Also make sure you don't put all your cards containing high aura in your deck as you have to wait for aura refils in order to summon them which will put you at a disadvantage during battle. Get in the habit of checking the card details for every character by clicking on the info of that selected card.
Check the Shop
Every twelve hours or so the shop will rotate so make sure you regularly check it at least once every day. At the shop you will be able to buy individual unit cards cheap which is useful if you are on the verge of leveleling up and just need a few more cards. Remember though that the rarer the card, the more expensive it will be.
Control Momentum of Battle
You will find that if you can control the 'momentum' of the battle your chances of winning will increase dramataically. Controlling the 'momentum' of battle means that you take the initiative and force your opponent into unfavourable situations you can take advantage of.
Leveling Cards
The most beneficial time to level up your cards is during the early stages of the game, especially when you going F2P (free-to-play). You will find that common cards can be leveled up easily as they are not difficult to obtain from matches or chests.
Premium Dust
The only way you can become competitive in this game is by spending real money in the shop on Premium Dust which can then be exchanged for either Lien or to open crates for high rarity cards. You can obtain Lien during gameplay but it will involve a lot of grinding.