I was steak cooking newbie but found some good tips online and finally made a little tutorial about how Nancy Does Steak!
Preheat a cast-iron skillet on high heat for a few minutes. Don't need to add any oil or anything. Turn the oven onto 375.
Prepare the steak. I "butter" my steak with goose fat (see ingredients picture below) and then use coarse kosher salt and cracked pepper, and plenty of both. The reason kosher salt is necessary is that it has big spikey crystals that will stick to the meat better than table or sea salt and that helps the meat form a crust (according to Alton Brown). If you don't have goose fat you could use another fat with a high smoke point like peanut oil. Don't use butter though, it burns easily.
(Look at all that goose fat! I had that whole container totally full from cooking one goose.)
Plop your "buttered" steak into the pan and let it sear on each side for 2-3 minutes. On this steak I went for 3 minutes. Turn on your vent fans, open your windows! You might want to use a splatter screen if you used a lot of fat.
Turn it over to the other side and sear it. About the time you're done searing your oven should be up to temperature (at least mine is).
Lift the pan off the stove-top (use a pot holder, it is HOT!) and put it into the oven.
How long to cook? It seems to depend on the thickness of the meat and the size of the steak. This one was 9 minutes to be pretty rare. You can learn to judge the doneness by poking the steak with a finger. If it feels mushy and soft, it is very rare. The firmer it is, the more done it is. I often like leaving it a little rarer because I eat half of the steak, next day I re-heat the leftovers and put it on a big green salad and I don't want it overcooked from the reheat.
Let the steak rest for 3 minutes and tip the platter so the juices run off. You want that "crust" you made while searing to stay as crunchy as possible. I'd suggest using a bigger plate than I did.
Optional Step 7:
Throw something like spinach or another vegetable in the pan and use the left over heat to cook it. You'll get vegetable mixed with yummy fat, salt and pepper with that lovely steak flavoring.
Enjoy! There's a side of avocado with mayonnaise if you're wondering about that green/white blob.
Everything I know about cooking steak came from these two sources:
Guide to cooking perfect steak
Alton Brown's steak method (video)