I also recently attended my boyfriend's sister's high school graduation. As part of her present, I wrote her a long letter with some advice on what to expect in college. There's some silly advice, but I wanted to make it not-so-preachy. My real letter to her was three pages long (single-spaced...whoops!), but here's an overview of what I wanted her to know.
1. Make sure to maintain relationships that make you feel good and let go of the ones that bring you down. College is the perfect time to weed out those friends who never treated you well but you had to hang out with because your other friends hung out with them. College works for this because you're away from each other for long periods and it's easy to say "oh, I had to spend time with family" when you come home for college breaks (which is true). No need to be harsh or mean, just slowly drift away if necessary. On the other hand, for the friends who make you feel good and treat you well, make sure you keep in touch with them and don't let four years go by in mostly silence. My best friends from home got scant word from me, with occasional visits. Now I regret not keeping in touch as much because it feels like I'm constantly playing catch-up with them. If they're important to you, make time for them.
2. Speaking of making time for people, you're going to be meeting a lot of new people, going to the dining hall with your roommate, walking to class with friends. But you will also be going a lot of places alone sometimes. That's the perfect opportunity to make phone calls to your family and friends to catch up. I didn't do this nearly enough in college, but now I call my parents and best friend while I'm walking the dog. It's a great time to hear from them and see how their doing and tell them about all of the exciting new things you're experiencing. But with walking alone, have constant vigilance. Campuses can feel safe and generally are, but it's best to always be aware of your surroundings. Especially don't walk around alone with headphones in at night!
3. This goes with number two, but it deserves its own category. Call your mom as often as you need to and sometimes more than you want to. While it sometimes got tedious and I had other things to do, my mom and I talked every single night when I was in college. We still talk multiple times a week and text every night. You might not do the same thing, but if you do, know it's normal and no one will make fun of you (or if they do, don't bother with them because they're jerks). I used to be pretty sheepish about it, but the more people I mentioned it to, the more I heard "I do the same thing!" Your mom will always be your biggest supporter and will the one who is always, unconditionally there for you. Your dad too, but there's something really special about mother-daughter relationships.
4. If you get homesick, it is 100%, completely normal. However, don't follow my lead and let yourself wallow in it and not enjoy your time in college (I cried myself to sleep every night first year--don't do that!). It's okay to cry and miss your home and your familiar friends, so when you're feeling down, that's when it's time to reach out to those important to you. Skype is an amazing invention and was made for homesickness. But don't let yourself wallow. Be sad for a night and then get up the next day and do something awesome that reminds you why you're out on your own. Go to a gym class, see a play, even study. Just get away from your room and do something fun for you. If you do that, the homesickness will slowly go away as your new school becomes your home-away-from-home. Homesickness will pop back up sometimes, but it won't overwhelm you.
5. In the spirit of getting involved and doing fun things, go to the school activities fair which usually occurs in the first week or so on campus. Explore different clubs and organizations that interest you. Just sign-up! There's no commitment if it turns out it's not for you, but just exploring something new can be fun. I wish I had done more of this in college, but even if you only find one organization you love like I did, it will make your time in college even more fulfilling.
6. If your school offers free gym classes, take advantage of them. Classes start costing $10+ once you get the real world, so enjoy the free ones while you can. I highly recommend zumba for a really fun, high-paced workout. Or yoga to start good, life-long habits. I find yoga dreadfully boring, but the health benefits are amazing. You're still young, but starting these habits now set you up for a life-time of good health.
7. If you don't want to drink in college, don't. If people judge you for your decision, they're not worth your time anyway. Most people won't care, but there will be some do--again, those people don't matter. If you do decide to drink, be smart about it. Don't go places alone, always use the buddy system. Never leave a friend alone at a party and never be friends with someone who would leave you alone. Sadly, constant vigilance is necessary. I have two stories that promote this idea. One time I went walking alone on the beach after drinking. I stepped on what I thought was a jellyfish (there were a lot during the day). When I got back to the house, everyone was asleep so I crept to the bathroom to get ready for bed. It was then that I smelled poop. Turns out, it wasn't a jellyfish. It was dog (or human?) poop. Moral of the story: don't walk alone when you're drunk. It's always a bad idea.
To be safe at a party, it's probably best to stick with a beer can that you open yourself. Which reminds me, do not EVER drink anything that ends in "bucket." A) You don't know what's in it. B) It was probably made in a trashcan or bathtub--clean or not. C) It generally tastes like fruit juice which means you don't taste the alcohol (and trust me, it will be loaded with different types and vast quantities of alcohol), which means you get shit-faced really quick because you think it's just fruit juice.
8. Take classes that interest you even if they're not in your major (but make sure you plan your classes so you take the correct amount and do all the correct prerequisites!). A course in recent history could teach you a lot about the time your parents and grandparents grew up in. A course in cultural anthropology will teach you about different cultures in the world and why people do what they do based on their customs (one of my favorite classes in college). In college, you'll meet people extremely different from yourself which will be a learning experience in itself. Enjoy listening to their stories because they'll give you a greater appreciation for things that may have never interested you before. With my advice on classes though, keep in mind that you shouldn't just take something because someone tells you that you should. It's up to you what to take, so try to find something that interests you, not just what your roommate, friends, or family want you to.
----
Those are my eight pieces of advice. I know there's a lot more to say (like when gossip inevitably happens), but those are personal issues that we all must figure out on our own based on what we think is right at the time. You'll go through ups and downs, but you'll get through them. You're strong and intelligent and have a caring support groups, so remember while college is an adjustment, you're going to be amazing.
School can get overwhelming, the food can get bland and boring, the people on your hall can be annoying, and the same routine can get stale. If you ever need a break from campus, know that friends and family are just a Skype, phone call, or short-drive away. The college years are wonderful and challenging; make sure to enjoy them.