To a certain degree you can't help it. Some dogs are naturally explosive for a cue some can be made explosive for a cue. Many can't. Some have naturally good grips and deep bites some don't and it can't really be fixed. Some don't have the nerves for the pressure they see. Some don't have the mental endurance to make it through a routine. Some wash out because once you put control on them they don't want to do the bite work. Some get their foot stepped on by a decoy or helper or whoever or bite their tongues during the bite work and then don't want to do it anymore.
Long story short it's like Blitz says. The dog is what it is.