A mix of sim and air time. It's far easier to learn the procedures and methods in the sim, without having to worry about the real world environment. If you mess up an approach in the sim, a press of a button puts you right back at the start of the approach, and you do it again. Not so in the aircraft where you have to book slots etc. Sims also have a pause button, so you can discuss certain points with your instructor at the time, look at the printouts and see where you may be going wrong.