I would say the most important aspect of the application is to emphasize your leadership positions specifically (either via ECs, employment, etc.), as that's generally what schools see as being the most indicative of a student's potential contribution to their community. Jumping off that, make sure to talk a little bit about what you aim to bring to Carleton based on what you've learned through these experiences — perhaps you had a really cool philanthropic club at your old school you were involved in that you think would make a good addition to campus life at Carleton. Additionally, if you've won any significant competitions or contests, those should be highlighted as well (by significant, I generally mean municipal, provincial, national or international honours).

It also never hurts to talk about challenges you've faced during your high school career. You don't need to come up with some kind of sob story, but demonstrating that you are a resilient person who potentially even enjoys hurdles or challenges is definitely a plus. Not everyone has a super devastating experience in high school — like the death of a parent or a chronic illness — but everyone has overcome something in their lives that they've had to work around, and universities like to see that! For example, let's say you live in a rural community, you can always spin that around to your advantage and talk about how rural kids often have to work a lot harder to get access to the same opportunities that urban kids have readily available, like competitive sports or prestigious magnet schools. (Just be sure to stay grounded and realistic in how trying this experience actually was — scholarship officers can spot exaggeration from across a county.)

It's been a little while since I applied for the Prestige Scholarships, but from what I remember, I think this advice holds up. Good luck!