Training for specific lifts is just as much of an art as it is a science. For example, there are lots of technical aspects that one needs to learn that are individualized. For example, when squatting based on your anthropometrics, you may want to squat wider, with more hip flexion or whatever else might be specific to you. When it comes to training for a specific lift, like a back squat, you need to take into consideration what muscles are involved in the lift and where you are actually lacking. For example, if you keep missing the squat at the bottom position because your low back cannot maintain stability, then hammering your quads on the leg press won’t necessarily help you get any bigger numbers on the squat. Your back is weaker than your quads, so you need to raise the potential of your back strength before your squat can increase. Then, next thing you know your back can handle a larger load than your quads and you have to switch back to more of a quad emphasis. This is the cyclic pattern of training that often takes place, but with a purpose. So if you are missing your lifts on a lift you want to improve, look at it objectively and understand why!