I really wish that there was a list of this stuff when I was an incoming freshman. Now, I've been through the entire experience. I have come up with a few tips for those 8th graders that will be entering high school, or for the rest of you who are just having a hard time, like I did.
WARNING: Don't read these as if every word is the word of truth. They are from my experience or that of my friends.

-Keep your head up when you're in the halls. It will keep you from getting bumped into. If your head is up, the people will *subconsciously* feel slightly intimidated and will move out of your way. If you keep your head down, you are more likely to be pushed out of the way.
-Do not procrastinate! I know how difficult it is to get started on a project that is due in 3 months, but don't delay! *bad experience... stupid ink cartrige that ran out of ink at 2 am on a 15 page paper... no joke.*
-Keep a meticulous assignment book. You will forget assignments. (This is true for middle school as well, but moreso for high school.)
-Make friends. Everywhere. High school is very cliquey *meaning, it has a lot of small groups of people that hang out*. Make sure that you have friends all over the place, especially in your classes. How? BE NICE. BE CONSIDERATE. People like others who don't say negative things about people.
-Don't stress out. When you get home, take a half hour nap, or have a snack and watch TV, check your email. Don't go over an hour, or you'll never get started on your homework. However, you do need a little while to wind down from the day.
-Do all of your homework. Every night. No exceptions. Finish it before you go to bed. It makes the next day much less stressful. Every point will either count for you or against you. You can't sweep it under the rug. It's in the gradebook.
-Do all extra credit available. Some teachers don't do it, but most do. Make sure to get every spare point you can. However, finish your other homework before starting on extra credit because homework is worth more in points.
-Make friends with the teachers. This will help you get a high participation grade, which raises your grade quite significantly (as opposed to goofing off) and it also makes them more lenient on you. Teachers are also good people to turn to for advice. You also need them to write your letters of recommendation when you're a senior, so don't goof off or cheat because that's what they'll write about!
-Be brave when it comes to relationships. High school is an open place, and people don't normally hold grudges all that long. They forget things because there is so much to remember! So, if you like someone, go for it. Give them your number. Go out to lunch.
-For God's sake, be a responsible driver. A student at my high school died in the fall of 2002 because he was in the car with a drunk driver, and he too, was drunk. His death was a great loss to the school, his friends, and his family. The event affected so many people. Don't repeat his mistakes, or the mistakes of his friends. The driver spent jailtime. DO NOT GET DRUNK. DO NOT GET IN A CAR WITH A DRUNK DRIVER. DO NOT DRIVE DRUNK. (Those last few are for everyone. It's common sense!!)
-Don't flake on your friends. That's the perfect way to ruin a friendship and make enemies. This happened to a couple of my friends. They now hate each other, but they used to be best friends.
-Don't mooch off of people. If you just forgot something one day, fine. But, be sure to bring it the next day and every day from then on. There's nothing more that I hate than someone who never has paper, pencils, a calculator, or the textbook. However, if somebody wants to borrow something, lend it. It won't hurt you or anything, and it will help them.
-Don't buy elevator passes or tickets to parties on the roof. The people selling the tickets are pranksters *usually seniors* who just want to make money from unknowing freshmen. *Our school has no elevators except for a handicapped one, and going on the roof is against school rules. There will not be any parties there.*
-Don't cheat. Period. You know the boundaries.
-Go to your guidance counsellor frequently. They will help you stay on track and they're looking out for your best interest and well-being. They can also write smashing letters of recommendation if they know you well enough.

Have I left anything out? If I have, please email me your tip!