Don't sit down at the back of the class and observe me teaching a whole class input, go and do something useful from the endelss list of jobs that need doing!
Don't chat to to other adults/TAs/kids while I am talking or trying to teach.
Do actually look at the plans if the teacher gives them to you, then you might know what is going on and how best to help.
If the teacher asks you to do sometihng every day, don't only do it on the days she asks you, do it every day without being asked!
If the teacher has shown you a system for where she puts sheets to be photocopied and laminated, and asked you to do it every day at 11:30, for goodness sake do it everyday, unless there is an emergency. Don't forget all about it until you are next reminded.
Use your initiative, you are meant to be assisting the teacher in her teaching!!
Don't shout at children for just being children, just because you will have to clear up the mess at the end of the day doesn't mean they should be shouted at for experimenting with paint and glitter and using their hands as paintbrushes. I like them being messy and exploring with all their senses, get involved, get excited at the active learning they are doing, don't stifle them by shouting...
Wish I had a good TA...