I feel like I am at least 50% qualified to share what doesn't work in high school as I have failed many times and succeeded some of the time. The following advice are mostly related to college as I am not qualified to give general life advice as I am going to be trying to figure that out for the rest of my life.
1. Taking the hardest classes possible to the point where you don't sleep is pointless.
Leave no sleep for college. I'm not advocating for people to not challenge themselves or take challenging courses; instead I'm urging high school students to be more balanced, because everyone knows that I was not really in high school. Also, if you take a smaller amount of college level courses, like 5 instead of 10, you'll probably be able to do better and learn more. Yeah, learning is more important than the long list on your resume.
2.Worrying about how "good" the college you end up at is.
I was raised with this ideology that if I went to Harvard, I'll bring so much success and pride to my family's name. I don't even know what that means, my family literally has three last names. Anyways, I am not at Harvard, but I am also happy and taking a small amount of L's at Lehigh. Please don't base your college decision on the opinions of other people because lets be honest, your Aunt Martha's opinion and your classmate Joanne's opinion doesn't matter, they're not paying for your college.
3. Adding activities and community service opportunities to your resume just to make it longer.
Are we really gonna believe Michael who was a peer mentor in D.A.R.E. when we really know what's going on? Be genuine, don't do things just to bulk up your activities list for the common app, no one appreciates snakes. Colleges will most likely see right through it as it's not difficult to differentiate whether someone is actually involved in a cause rather than using it to seem more accomplished.
Sometimes trying too hard is a real thing and we really need to just "wear life like a loose garment" more, kind of like Yoda's jedi master fleece robe. Trying to control inevitable results will simply create many problems that you don't need senior year of high school, or ever. I swear I would usually not take my own advice, but this time I'm actually spitting some facts.