Off the top of my head I'd reccommend the following:
-Learn the layout of where everything is stored, even if it's just a rough plan with the like of 'physics stuff', 'circuit stuff', 'biological chemicals'... It'll save a lot of time running around looking.
-When I'm training new tehnicians I ask the teachers to be very specific in their orders. Insted of writing 'limestone cycle prac' I get them to list every piece of equipment they need so the technician has a exact idea of what's involved rather than having to look it up themselves (though there is a learning experiance there, if time permits).
-don't try and take shortcuts if you're short of time, such as using a stronger acid to produce Hydrogen Gas because it'll be quicker (I'm speaking from experiance). follow the safety advice and if it takes longer, explain to the teachers that they'll have to be paitent until you are more familiar with the activity.
-make sure you know where the Cleapps handbook is and how to use it. Same for the Hazcards and Recepie cards. If you don't know what somthing is or how something works there's probably a guide to it on Cleapps.
-Make sure you know what's expected of you. Are you expected to photocopy? trail practicals? order and maintain stocks? Are you expected to take break or lunch duties (this shouldn't be part of your job description and if you choose to do it you can expect to get paid to do so)? It may sound a bit pissy but that kind of thing can have a massive impact on your time.
-Remember that you are not legally responsible for risk assessing the practical lesson in the classroom or what happens in the classroom, the teacher is. Assuming everything you have prepared is safe and correct (and you've provided that information for the teacher) you cannot be held responsible for accidents or injury in the classroom.
Despite all that though, the job is incredably varied and sometimes doing something that's not expected of you (school trips, demo's in classrooms, extra-curricular activities) is great.
Hope this helps.