Hey, Clev! I'm Clair. :)
I'm 16 and I made the switch from homeschooling my whole life to public school last year/spophomore year. My experience was pretty great. If you keep a positive outlook, you'll do great.
*Disclaimer: You don't have to listen to anything I say
First off, I would make sure you have someone show you around/take you to your classes. In my experience, and in my siblings', their counselor always arranged for someone to help out (usually a student), but if they don't, just ask. You don't want to get lost! :)
I would try to make friends your first week. Depending on what grade you're in, this may be kind of hard (i.e. if you're a freshman, no one really knows anyone, so making friends should be pretty easy). Also, if you're really introverted (heh like me o_o), this could be difficult. I guess since it's halfway through the year, don't be surprised if it takes a little while to make actual friends. Just be friendly and engage with other people, instead of expecting people to make the first move.
Find someone to eat lunch with! Preferably a couple people, so if one person is absent, you won't be lonely. If you do end up in this situation, but don't feel like looking like a loner, just go to the library. :P
Be prepared to get sick. You might just get a small cold, like the one I got, but I have friends that would get the flu like every other week when they first made t he switch.
If you feel comfortable, try introducing yourself to your teacher and let them know about stuff that would be nice for them to know/make them like you (even if you're a great student and they're a great teacher, I've found that some teachers assume that you're just like every other student). For example, I told one of my teachers that, at the time, I had no phone (I really don't know why???). That benefited me because when she would have the class take pictures of the board, she would always make sure someone sent a picture to my email or something.
You don't have to tell anyone you used to be homeschooled if you're not comfortable. Some people might think it's super kool, though.
If your teacher(s) assign homework, and explain to them your situation, they'll probably give you a little bit more time to finish it/turn it in.
No one's going to make you stand in front of the class to introduce yourself, like they do in movies. If they do... good luck. o_o
If you do end up making the switch, I hope it's a smooth transition! :D