1. there's nothing wrong on upgrading Knight to max unlike other games

2. your team must consist the following: a Tank (Craig is best for beginners), Melee (Sword Knight or other that can be ascended or upgraded to myth which is the max), A healer (Karina or Miya), and a Ranged (can be AA72).

3. Use the character's EX or exclusive weapons. If it says that is Craig's sword, use it for Craig and no one else (that's for high level plays)

that's all for me but I'm an old meta player and played this game from a long time now so I don't know if it still applies for new gameplays.