Simple enough, play 2 Bruiser / Dragonmancer so that you have enough frontline as well as damage early on. Make sure you make Karma your Dragonmancer Hero. DON't level up and go on a lose streak.
DON't level up to 6 until you hit Karma 3 on level 5. By level 6, you basically will have your core units and traits active. Level up to 6 latest at stage 4-1.