Early Rounds: Activate Warrior (3) Synergy effect, or Goblin (3) Synergy effect, or Cave Clan (2) Synergy effect to win in the early rounds. Remember to Buy Exp at Round 5 or Round 9 to make sure you can have more pieces on board than your enemies.
Mid-rounds: Keep leveling up to reach Lv.7 at Round 15 and meanwhile keeping 20 Gold at hand for Interest. At this stage, you may deploy some 2-star pieces that deal AOE Magical Damage, such as Shadow Devil and Thunder Spirit etc. Reach Lv.8 at Round 20 and keep more than 10 Gold at hand.
Later Rounds: Upon reaching Lv.8, try to activate Mage (6) Synergy effect. If failed, always try to replace the on board pieces with your main ones, and meanwhile, rank up the deployed ones.