Pretty much what Kyosuke said, focus on all your teams equally, and when you reach a point when all your teams can handle difficult maps (with this i mean killing a few pests of ?-8 without getting rekt) then you can power up your helper squad, atm these are my squads



Now they are pretty balanced, but a while ago my helper squad was too far strong from my other squads, and i was strugling with event maps cause my other squads where so damn weak, so improve all your teams equally and you will see the magic