Not sure if anyone will properly answer this post, but in general, as long as you put in the time and effort (e.g. attend lectures and tutorials, do your readings, past papers and revision, et cetera...), then there shouldn't be any problem with getting an HD (especially for first year subjects).
With WAM boosters, what works for others might not work so well for you. For example, I read that HPSC1000 Bioethics was a WAM booster for science, and I only just managed an HD in it (I was getting marks like 73 and 84 in a couple of the essays). In my opinion any first year calculus course would be a WAM booster, but I'm sure there are many who would disagree with me on that. It really depends on what you are good at.