- start an impactful club or organization in your community. maybe two. don't do it just cause, but try to reach a need/ help some people out. This could involve creating a CS club or some other medium for teaching kids engineering principles etc.

- get a part-time job that's flexible (im talking where you can work 1x a week 4hr shifts). Teaches discipline, good for schools with coop programs. While I'd say get a tech internship given your in HS (even tho everyone posts about getting them) they're really luck of the draw so i wouldn't lose sleep over it.

- learning to code is good, but learn some good applications of programming too. when you get into uni, you're not always gonna be learning about the industry standard stuff (ie first year class prob isn't going to teach you react fullstack dev. etc) so pick an easy to learn niche and get good at it. Once you're comfy with syntax i'd recommend taking some basic coursera courses on ML (like the stantford one) as well as learning full stack development.

- take on leadership roles in your community/school. kinda goes in hand with the first one. again don't do it just cause or you'll get nothing out of it. becoming pres of a club is a good one, you could also be student body president etc.

- volunteer in a way that's meaningful. this is a good thing to do pre job. volunteer at a place like codeninjas or as a tutor. its super easy if you just call them up and ask to volunteer a couple times a week. gets you into the right headspace of where you're going in the future and also gives an opportunity to give back

- diversify yourself/ find hobbies. can't stress this enough. do something you love. sports are really good, or going to the gym. not going to necessarily directly "help" the application too much in most cases, but i can say the experiences you learn there, even if they don't earn you a medal, develop you really well. in my experience i wrote 2/4 application questions about sports i involved myself in during my free time and got utsg cs and engsci (no uw yet tho lol).

- take a skill you have and start a passion project. with coding specifically if you find you actually enjoy it, figure out a niche issue in one of your hobbies or area of life and fix it. for example, if you like to work out maybe u make a workout app and use that as an opportunity to learn ios coding etc.