honestly your year 8, 9, and 10 electives don't really matter for picking HSC subjects UNLESS you plan to take a language continuers course, for which you must complete the corresponding stage 5 language elective course.
if your school offers accelerated HSC subjects as a year 9 or 10 elective and you think you'd be able to perform well in the offered course i would definitely suggest trying it out as you can always drop later and if you end up completing the course with a good mark you'll be a lot less stressed in year 12. they also give you an opportunity to learn how the prelim and HSC courses are structured, how internals and externals work and how to manage stage 6 coursework.
if you're completely unsure of what to do and think that you're more of a english/HSIE-centred student then i would personally recommend taking commerce if your school offers it as it gives you a brief intro into HSC subjects like legal studies and economics.
besides that though, if you're more of a STEM student then perhaps pick electives related to the sciences you want to pick up or in general just go for what you're truly interested in because junior electives are kinda the last time you can just take a subject for fun.
scaling doesnt apply/matter for junior school electives so im assuming you're referring to what HSC subjects scale the best. in general harder maths and science courses like math ext 2 / ext 1, chemistry and physics scale very high. for languages the top scalers are latin continuers and latin extension (and i think most language extension courses scale well in general). english ext 2 also scales pretty well, eng ext 1 is high but not as high as chem/phys. the highest scaling HSIE subjects are modern history with history extension and economics.
however (and ik a lot of people in y10 may hear this a lot and disagree with it until they actually get to year 11/12 and realise the truth behind it) i really think its much more beneficial for you to choose subjects you're already good at and know you can do well in (even if they don't scale extremely well) rather than harder subjects just because they scale well. in general if you go to a pretty good school and can maintain top 10 ranks in all your subjects you're much more likely to achieve your goal ATAR than if you took a bunch of harder subjects that you don't enjoy (and thus won't be motivated to study for)/aren't good at just for the scaling and end up with average to bottom half rankings.