Firstly and most importantly, a good cut of meat, I have the luxury of having a great butcher in the village, just don't go to tescos, sainsburys or asda.
A pretty vital stage is letting the whole steak reach room temperature, so this means leaving it out of the fridge for quite a while, it'll still be fairly cold and stiff after a few hours, I try to give it all day if I can.
Next, heat your frying pan up to a high heat, and melt a large knob of butter in it, if you have a good cut, you don't need any other seasoning.
Fry it for a couple of minutes per side depending on the size of the steak, 2-3 minutes a side will do for most average sized steaks.
Once you've done that, rest it in a 80-100c oven, on a rack ideally, anything from 5-10 minutes depending on the size of the steak, 5-7 minutes should do it for your average sized steak.
This will give you a perfectly cooked rare steak with an even temperature throughout, if you want it medium, just add a minute or two per side when frying it.
If you want it well done, just fry it in the pan until it's tough and dry, you don't deserve a nice steak
I also like to fry some whole mushrooms in butter as well, and cut and butter some lovely bread, a great meal.