First things first, decide who is important to you. Does it really matter that a gaggle of people you'll never see again after high school called you Morticia as an insult or ask who died? I promise you, it doesn't. Accept that some people are just going to be rude no matter what and ignore them as best you can. You might find that they parrot all kinds of misconceptions about Goths which you might wish to dispel, but it's not worth it for every passerby. You'll lose your voice before it penetrates their thick skull.
The build up to "what are my friends going to think" is the thing I know a lot of babybats are worried about. Your friends may or may not find this whole Goth thing weird. If they're totally accepting and don't mind at all, I'm very happy for you. You're lucky and those are some good friends you have there. You might even be lucky enough to have other Goth friends at school, or friends that (now that they've seen you start to dress how you like) will also come out of their shell. However, not everyone is so lucky.
If one of your friends decides for whatever reason not to support you or remain your friend now that you're dressing Goth, this can be very painful. However, as I'm fond of saying, a friendship that ends over something this trivial isn't a friendship that you should be bothering with. Of course it's not going to be easy if you share any kind of history, but keep your spirits up and I promise it will get easier. You can try to explain what Goth is, expel the rumors and that, but after a while you're going to have to let friendships go that don't better your life.
Know who your allies are. If the rude comments of other people start to go into the bullying territory, you may wish to seek the help of either your school counselor or a trusted teacher. Knowing who the people are in the school who will take your complaints seriously and building up a healthy relationship with them can make some of the issues easier to manage. Remember: it's not weakness to need help.
Readers, what advice do you have for Babybats who are going back to school Goth for the first time?