The key to good flank steak is to cook it fast over high heat and keep it medium to medium rare. When cooked and rested, it is very important to slice the steak across the grain of the muscle fibers. If you don't do this, your flank steak will be very tough.
Before cooking, marinate the steak in your favorite marinade.
You can cook it on a stove top grill, under the broiler or in a skillet.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan