Consider using the Augmentation on unwanted characters. Augmentation sacrifices a character in order to power-up another character.
Fighting
Enemies will flash red just before attacking. After a couple of attacks of your own, be ready to dodge roll out of danger by swiping the screen. Each character has a certain elemental affinity. Red elements are stronger than green elements. Green elements are stronger than blue elements. Blue elements are stronger than red elements. Purple and orange elements are neutral to each other. You are given a preview of what type of enemies you will face at the stage select screen. Include a character that has an elemental advantage over them.
Orders
The "Orders" option can be found at the left side of the main menu. They are optional objectives. There are four types of Orders, daily, weekly, free, and event. They correspond with how long you have to complete them before they reset. Complete them to get coins, soul tickets, and other valuable items.
Soul Tree
Each character has their own "soul tree", which gives them a permanent increase to their stats. Power crystals are used to unlock the nodes on the soul tree. They are found by destroying objects and defeating enemies as you progress.
Spirit Orbs
Spirit Orbs are used to get new characters. They are obtained by completing events and earning all the stars for a level. Do not waste them on replenishing soul tickets.
Stars
There are three possible stars that can be earned in each level. The first star is rewarded for completing the level. The remaining two stars have special conditions that must be met. Each star earned on a level will result in a precious Spirit Orb which can be used to summon more allies.