I think it's a very good book. The approach Harold Gusking uses is similar to a Meisner repetition exercise, at least that's how I see it.
With that in mind treat the script as if you are practicing with another actor.
The premise is clear and simple: work off the impulse moment to moment. In other words whatever hits you in the moment is exactly what you express. This teaches to concentrate on the present moment.
The other benefit is you train yourself to work off the script in a very relaxed way without pushing for an obvious result.
