So I'm probably the most out of touch here as I graduated in 1995. There wasn't even internet at my school while I went there. As such, I imagine the experience is completely different. That said, some stuff is liable to be the same, so take the advice of someone who didn't do these things:
- stay current with your assignments and homework. Some teachers let me do catch-up at the very end of the semesters, but it was 0% fun and not worth full credit
- don't ditch a lot if you can help it. It ties into staying current with your schoolwork, but also makes it harder to maintain tight friendships. This might be different nowadays with phones keeping people connected, though? Not sure. (I ditched *a lot*, it was fun but I paid for it long term)
- keep in mind that in general, people are more worried about themselves than they are with whatever you're doing, as long as you play it cool. Someone who acts up a lot will probably find trouble and be remembered for it, but a few years out of high school, no one remembers that someone tripped or did something dumb. I know at the time, it seems like it's the end of the world; it isn't. Just do your thing and as long as you're polite and cool, good things can come your way.
Good luck! It's easy to get discouraged but take it one day at a time and you'll do fine.