1) Plan the long term goals before you organize the daily details, but stay flexible enough to change those plans if one or more students suddenly need something different.
2) Prepare so you'll have answers for all the random questions you might be asked in class, but be honest enough to say when you don't know an answer. (Then go home and find the answer for the next day!)
3) Speak firmly and naturally, but not until students have given you their attention. (Firm and natural eye contact and body language will probably help you get their attention first.)
4) Be open and sincere with your students so that they see you are a real person with feelings just like they are, but be ready to put aside your personal bad day when you step into the classroom.
5) Maintain open communication with parents, but discuss difficult situations with students first whenever you can.
Bonus #1) Be ready to feel like the lone adult for most of the day, but seek out opportunities to give respect and encouragement to all of your school's employees--other teachers, specialists, secretaries, custodians, counsellors, even administrators.
Bonus #2) Drink water throughout the day to stay hydrated, but be prepared to hold it since teachers are not in charge of their own bathroom schedule.
I really believe teachers should be lifelong learners who aim to teach students, not subjects. (Ok, maybe that's bonus paradox #3...and #4. Sorry...) So I always welcome questions and suggestions for my writings!