Okay I am a few weeks away from going to college. So my perspective on the last four years...
I guess if I could give you a single piece of advice, it would be this: Chill out.
You're at a point in your life where all kinds of stuff you are doing might seem like it really matters. But just take some time to think about what is really going to matter in the long run. I know you hear that a lot, but actually sit back and think about it. Think about it. No you still aren't thinking about it. Don't read any further until you have thought about it!
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Among the things you will have forgotten before you've even left college: Your social status this month, the girls you do or do not get with, the teachers you hate (you might remember the good ones), the friends you hang out with on a daily basis.
I can tell you honestly that I have a hard time remembering who/where/what I did in general freshman/sophomore year. Without a lot of thought, I couldn't tell you my five best friends. And I just realized the other day that I can't remember a SINGLE class from that year. They have all blended together, and I'm not even three months out of high school. I asked my Dad the other day if he could remember any high school friends. He remembered ONE name, and that was tough. He remembered two teacher names. So what I'm saying is, don't sweat the small stuff, or even the big stuff. Nobody is going to care about it in the long run, not even you.
I guess I'm pretty far into this and I haven't mentioned the one thing that WILL matter in the long run - your grades. In four years, you want to be a shoe-in to a major university. Nobody needs to go Ivy League as an undergrad (short for undergraduate, or grades 13-16), but you do need to get into a top-100 school if you don't want to be playing a LOT of catch up later on in life. I know it's hard to see the connection between high school grades and your life as an adult, so I'll just make it easy for you. If you consider yourself a smart kid, you need to come out of high school with a 3.5 GPA . That's half A's and half B's. If you consider yourself to be decently competent, but not the shiniest apple of the bunch, DONT WORRY. All you need to do to be even with (or ahead of in many cases) the smart kids is work 20% harder. Get a 3.7 GPA and you'll be fine. Junior year you will take the SAT or ACT and score a bit lower than the smart kids, but your GPA will make up for it.
That's really all you need to do. The rest is gravy, but remember, in five years you won't remember 99% of it.