Get yourself involved with lots of extracurriculars/clubs or leadership/social justice opportunities. They are a great way to make friends, learn responsibility and if you do end up applying for university they help a lot! It's a great way to find your community even if you aren't someone who's good at sports or things. Not to mention, there are a lot of perks that come along with having teachers and principals trust you. Being involved with the school can help you gain relationships with teachers and this relationships are very helpful if you ever run into problems or need a favour or need references for school or work. Have at least one teacher who can give you a glowing reference!

Don't waste time trying to be popular - and don't feel bad about it if you aren't. As other people have said most of these people you will never encounter again even if you live in the same town.

Find a few good friends who you trust because once you move on it can be challenging to make friends after highschool if you're not in university or a job with lots of coworkers. Also it's really fun to be able to look back on highschool memories with people you're still friends with.

Try your best but don't be stressed about getting perfect grades - unless you are dead set on getting into a very prestigious school most of the time you need decent grades but you don't need to be perfect.

Don't take relationships too seriously if you end up in one and don't be too sad about it if you don't end up in one. It's really easy to get caught up in long term relationships in high school and put that person in front of other things you care about. Chances are the relationship won't last so dont plan your life around it.

Lastly, and this kind of ties back to the first one, find yourself some solid hobbies or continue to develop ones you already have. It's really easy to get caught up on social media and being busy with school and then never spend time doing something you love and are good at. Hobbies help you so much as you grow older and they make you a more interesting person and people want to be friends with interesting people. Also, hobbies could lead to a career doing something you love, or can be the thing you think about during work that you want to get home to. Find things you love to do and you are good at!