I think we used Loveland for Public Law (Con & Ad). I didn't do any preliminary reading for the GDL to be honest. I'd just skim read it if I were you, then worry about the specifics when your tutors point you in various directions.
You've got the interpretive approach for statute correct. Let's use "the cat sat on the mat" as an example:
Literal Rule
A feline is in a sedentary position on a fabric item commonly described as a 'mat'.
Golden Rule
...but the above interpretation is nonsense - surely this suggests the mat upon which the 'cat' is sitting is floating in midair?
Their Honours, in this case, interpreted this as "A mammal, described as a domesticated cat, recognisable as such, is sat upon a mat, which is placed upon the floor of some nature, in such a way as to ensure there is no separation of cat, mat, and floor.." This has become known as "the doctrine of feline sedentation."
Purposive
The phrase analysed has the intention of being a description of a position of a cat when not walking.
Mischief Rule (Heydon's Case)
The 'spirit' of the above sentence is that a mammal takes up a sedentary position, whether mounted upon its posterior or reclined in any way, that the cat, or other species which may be denoted as a 'cat', upon the floor. The 'mat' of course, may be construed to mean any soft floor, which could of course be simply carpet, or regarded as a minor part of this sentence, the importance being that the animal itself has placed itself upon a floor of some nature, regardless of its composition, or the presence of a separator between the 'floor' and the animal itself.
Something like that.