3.1 Key Pointers you must know in a fight
1- Some skills can interrupt opponent skill.
This so important as if you can time your casting properly, you can cancel opponent skill and prevent tons of incoming damage which is vital for crucible of fire stages. Not only so, you must know your opponent sequence of casting, so that you know when you won't be stopped from casting. Common interruption skills are Ember, Eva, Kane, Noire third skill for example. Also, a critical physical or magical hit can interrupt casting as well!
Example of how timely casting can win a fight, imagine 2 teams of the 5 starters fighting each other. On the third turn, Ember Eva Kane and Noire are gonna cast their skill. If you time the casting of Captain perfectly, shipwreck hits opponent Captain, Kane and Ember while the red circle is shown, you stopped 3 skill attacks from the opponent team which is enough for you to win the fight on a equal setting!
An example in the picture below, I activated my hydral and started channeling, somewhere 3.5-4s after activation, I casted BoMo's 1s to freeze opponent. As you can see in the picture, I successfully interrupted Lumina's Esclipe (you see the moon but my party hp is full) and Medusa's glare. I then follow up with Statik 1s to finish them off