I'm doing 3/4 Legal this Yr, without having done Legal 1/2. I'm already outsmarting every single Legal Studies student in this subject, and there's a student who did Legal 3/4 this year and, after previously doing in Yr 11. Anyway, the content is fairly striaght forward, and the only thing you have to do is outting the effort in to it and READ THE FREAKIIN TEXTBOOK!
However, be srue to get key concepts such as the Consitutional Referendum process in your head, because it can really become confusing for some (trust me when I say that people mention the right stuff but leave out the other bit - that is, A Referendum must obtain the MAJORITY of votes in the WHOLE OF AUSTRALIA, and A MAJORITY IN AT LEAST 4 OUT OF THE 6 STATES).
Quite frankly, the only situation when 1/2 is helpful is when you do Maths and Science.