Look at the Colour
Perhaps the most straightforward approach is to have a look at the colour of the meat inside the steak. On the underside of the steak (the side that will face the plate), cut a little slit down to the centre of the meat and have a peek inside. When it’s cooked just the way you like it, turn the steak over and press the surface with your fingertip. Note how it feels so that next time you won’t have to cut into your steak.