Place your Questors strategically. For example, you will begin with a knight, archer, and witch. Because the archer and witch are ranged units, place them in off lane positions. Position a knight or other melee Questors near the ranged Questor to hold enemies there so they can be hit with the ranged attacks.

After completing level 5 or 6 you will have access to the Healer Questor. Have her manually target another Questor, and she will heal them from time to time. When a Questor's health drops to zero, they will be temporarily knocked out. They will regenerate slowly over time, but you can use the Healer Questor to get them up faster.

Upgrade your Questors with cubes when possible, especially by level 8 when your enemies are noticeably stronger.

After completing level 11, you will be able to evolve your Questors. This requires two Questors of the same type. Select one and choose "Evolve", then select the other Questor to fuse with. You will be able to preview the result before starting the the evolution. If the questors you are fusing are upgraded, the final evolved form will have higher stats than usual. Thus, it is best to fully upgrade your Questors to level 5 before you evolve them.