Read everything you can on the subject you plan to teach. Being a good teacher doesn't mean that you have to be a genius, but the more you know going in to your experience, the better you will feel about teaching it and the more confident you will be.
Make contact with your master teacher and your field supervisor as soon as you know who they are. Don't wait until a few weeks before student teaching begins; make contact with those in charge of your student teaching experience as soon as possible so that you can build a relationship with them. You will be leaning on both your master teacher and supervisor a lot through your student teaching experience, so it is helpful to have a good rapport with them as well as established trust.
Visit the school you will student teach in as soon as you get your assignment. Find the guest parking lot, the building you will teach in, and if possible, the classroom you will be spending your student teaching experience. The more you know about the layout of the school the more comfortable you will be when you are teaching there.
Schedule a meeting with the principal. Principals are often busy, so be sure to do this as early as possible. Your meeting need only be a few minutes long; a quick introduction will suffice. Remember that if you do well during student teaching, this is the person who is likely to decide whether you are hired.
Buy clothes to teach in. Remember that as a student teacher you must go the extra mile in all you do, including in your dress. Be sure that you purchase clothes that are comfortable, but that are also formal. By dressing formally for class you will show your students and those you teach with that you are a professional who takes your responsibilities seriously.
Write mock lesson plans and practice in front of your friends. The more comfortable you are with relaying information, the clearer you will be in the classroom.
Practice your teacher voice. Most student teachers speak too softly at first; practice talking loudly in a large room so that you become accustomed to the sound.
Purchase vitamins and herbal teas to boost your immune system. If this is your first time back in a classroom since you were a student, you are likely to get sick during student teaching. Give your immune system a boost ahead of time to prepare.