I start my student teaching tomorrow...
But I really just want to sleep for a couple days...
What a dilemma.
I dunno if you're going to see this before you go off to your student teaching, but lemme give you a little bit of advice.
First off, don't be afraid if you end up fall in love with the little *** (Platonic love, you dirty people). The kids I student taught two years ago are graduating in May and there won't be anything that stops me from seeing them off. I still think about the classes I taught from time to time. Also, Juniors are awesome, so don't even fret.
You're jumping in halfway through the school year, which means they have to get used to you, especially because you're supposed to take over everything in the class in a few weeks (I say supposed to because not all mentor teachers enjoy giving control to a college student). They've had half a year to create a dynamic with their teacher, and you're going to change that.
They're gonna test you. They're gonna push you. Honestly, my biggest issue (still is) was discipline. You've got to establish yourself as the authority in there, but remember the line between fear and respect. If they fear you, they'll do what you ask begrudgingly. If they respect you, they're going to trust that you're taking them in the right direction. I don't mean be soft. Just be fair, be consistent and don't take ANYTHING personally.
Don't be discouraged if you work hard on a lesson plan and think it's perfect only to have the kids act out and basically hate everything from it. I've had that experience happen more than once. Because of that, I've reflected on what I did wrong and what the kids like and I've changed things up because of it. Always reflect on your craft and improve. Also, we like to use this term out here: monitor and adjust. If it's not working, don't be afraid to change things up on the fly. I have and it's worked awesomely every time.
Finally, have fun. Take some risks and try something new and different. You still have the safety net, so unless you do something outright stupid, don't be afraid to change it up. That's the best way to learn.
Good luck and enjoy yourself, sir! A really fun/daunting/terrifying/exhausting/amazing/honorable career awaits.