In a small bowl, combine flour, broth, sugar, and soy sauce. Stir until sugar and flour are dissolved. In a large skillet or wok over high heat, add beef, broth mixture, ginger, garlic, and broccoli. Bring to a boil, then reduce heat. Simmer 5-10 minutes or until sauce thickens, beef is heated through and broccoli is tender-crisp.