Red wine vinegar
Trim the fat off the flank steak. Cover the bottom of a glass dish with 1/2 red wine vinegar and 1/2 Worcestershire sauce, and sprinkle in the other ingredients to taste. Set the meat in the dish and marinate in the refrigerator, 1-2 hours per side (more is OK).
If you're using a barbecue, set it up for direct grilling. Grill about 7-8 minutes per side. Let the meat rest about 10 minutes when done. Cut the meat against the grain in thin slices and serve.