Use them on defense against cards that can't hit air, like Mini P.E.K.K.A, Prince or Hog Rider. On offense they add damage behind a tank or as part of an air push such as Lava Hound. If they reach the tower they deal damage fast.
Tips
Pressure with Minions right after your opponent uses Arrows or Zap.
Drop them right on top of a ground troop to shred cards that can't touch them.
Don't fly them in a group into the range of splash cards like Wizard or Executioner.
Strengths
Very efficient against ground cards that can't hit air.