Another good strategy is to not use units in the early game and keep drawing cards until you have a lot of gold income. Then you send a mass amount of units.
A very good strategy is to pick holy paladin starter deck, then use the card that makes it so that every time a unit is killed, the opposing side loses 1 health to their portal. Now send a mass amount of weak peasants and they will die and your enemy will lose health. It is like a short cut. Of course the determining fact is if you have enough materials for the card that makes opposing side lose health when they kill a unit.
 "Tyrant"){kind=icon}
 "Dream World"){kind=icon}
 "Shattered Colony: The Survivors"){kind=icon}
 "Hack Slash Crawl"){kind=icon}
 "Cardian"){kind=icon}
 "Demons Took My Daughter"){kind=icon}
 "Warlock's Arena"){kind=icon}
 "Dungeon Developer"){kind=icon}