ADVICE - I need advice as a new teacher going on placement soon

So I figured there's gonna be a bunch of students here haha...
I'm currently training to be a teacher but I'm struggling a bit with classroom management because I'm a pretty meek small Asian female. I went to a school where all the students were pretty well behaved (did a pretty hard test to get into) but public schools are an entirely different matter.
So, does anyone have advice for controlling a classroom (co ed public school). I learnt a few methods in uni and watching other teachers but I'd love to have more advice. What have you seen your teachers do which has worked? How would you stop kids from playing on their phones? Not handing in homework?
I've been working on speaking louder and being more confident but I'd love more tips because I want to do my best haha :) !