The key is to get the pan, or the grill, as hot as possible. Then psht! Psht! Both sides for like 2 minutes, and let it rest for 10 minutes. It’ll continue cooking as it rests. It’s important that the steak be at room temperature before you start, or you’ll have to burn the outside before you can get the inside to the proper temperature. If you cook it until the internal temperature is the desired temperature, then it’ll be overcooked by the time it is finished resting. It definitely takes some experience to get it right.