Pat the flank steak dry with paper towels
Trim any excess fat or silver skin
Season generously with salt and black pepper
Add optional marinade if desired
Let the steak sit at room temperature for 20 to 30 minutes
Preheat a grill, skillet, or broiler to high heat
Lightly oil the cooking surface or the steak
Cook the steak for 4 to 6 minutes per side for medium-rare, depending on thickness
Check for desired doneness with a meat thermometer if needed
Remove the steak from heat and rest for 5 to 10 minutes
Slice thinly against the grain
Serve immediately