How can i prepare my chances to study abroad?

I’m currently in my second last year of highschool in australia and i honestly don’t think my scores are going to be amazing next year due to not studying much (i work two jobs so 40 hours on top of highschool) but next year i plan on locking in at school. what are some other things i can do other than get decent grades (what kind of grades should i aim for if i plan on going to canada or somewhere in the uk for university) and should i do some extracurriculars like community work? is it cheaper/better to do one year at an australian university then go through that university to do an exchange for another year or two with that company? (do i have to pay for university in that country before i leave there or can i do some kind of debt payments) what university in victoria is good for those kind of programs? i know i still have a year and a half before graduation but i want to know what goals im reaching for so i know what i need to achieve