At the start of each combat round, determine initiative by rolling a d6. On a 1-3, all of the enemies will act first. On a 4-6 all of the PCs will act first. Reroll initiative each round.
Designer's Note: Using simple group initiative speeds up combat, keeps all of the players engaged, and avoids bookkeeping. Rerolling initiative every round makes combat more dangerous, since it’s possible for one side to go twice in a row.