Mix all ingredients for the marinade in a large bowl: olive oil, soy sauce, lime juice, and sugar
Put your flank steak into the bowl and get it completely covered with the marinade. Refrigerate for 30 mins to 2 hours, covered
Pat dry the marinated flank steak with paper towels and add salt and pepper to both sides. Remember not to add too much.
Heat up your outdoor grill or griddle until hot, and cook the flank steak for 6 minutes on each side or until the internal temperature reads 130-135 for medium-rare or 145 for medium.