I'm going to make the first tip post an obvious one. Get to the school early. No need to be there insanely early (do not get there before the custodian - how will you get in?!?). I like to arrive anywhere between 15 minutes to 30 minutes early. This gives you time to read the plan for the day, do any photocopying that the teacher has left you, find the attendance sheet, and locate the staff washrooms.
If you aren't going to get there early for any of the above listed reasons then get there early because you likely want to be a teacher someday and this is just a stepping stone to that job. Arrive for the job you want (not necessarily the job that you have).
Having said all of this... yes I have walked in to the sound of the bell (alright, it was actually the sound of the announcements and "Oh Canada" but what can I say the parking lot was confusing and it only happened once (thank goodness).