Marks are NOT everything. High school is NOT everything. Way to put pressure on, emacknight. Sheesh.
Mind you, grades are more important than the right clothes and much of that other junk. But don’t overstate the importance of high school. Keep perspective, like someone else said. Hard as it can be, it’s worth it.
To wit: a subpar test does not equal failing a class does not equal being rejected from the college you want does not equal your life is ruined. One of the South Park guys makes some very trenchant comments about this in Bowling for Columbine, actually - who you are in high school is NOT who you are for the rest of your life, don’t make too much of it.
Being yourself and seeking the truth is a great motto for life, not just high school. Play the game when you have to, but don’t be afraid. Don’t let certain people (mostly administrators, but the odd teacher as well) trample on you because they think they can. They are there to help you. They may forget it, but it’s YOUR education. Know your rights. I suppose this lesson is the main one I wish I’d known in high school - not that everyone was out to get me or anything. Just that as a kid in high school, you’re a bit afraid of the administrators and other jerks - bullies and things. They can really only hurt you as much as you let them, try not to give trivial things too much importance.
I’d say be friendly, be social, but be yourself. People who reject you for being nice and honest aren’t worth having around in the first place.
Do some activities - don’t resume-build compulsively, 'cuz it’s annoying ;), but try things that interest you and get involved with the ones that matter. You DO NOT need to pick a career by any stretch. But activities were what made high school worthwhile for me. There’s some room for nearly consequence-free experimentation in high school (I’m NOT talking about sex here, if you want to do that, be careful) when it comes to activities. When it comes to people, treat them well and you could make some very important friendships.