Good luck in your practicum! Be yourself and show that you care about kids.
How you dress depends on the school you work in. I have typically worked in smaller schools with students from farming families and students from lower socio-economic homes, so I tend to not dress too fancy. I still dress professionally, but there are many ways you can make jeans and leggings (as long as you have a longer shirt) look professional, whether it’s with boots, a (not too fancy) blazer, etc. See what the other teachers are wearing and try to be one above that (as a student teacher) and still follow your own style.
Good luck! 🙂
Teaching In Real Life 