This is something a lot of people worry about when they go back to school, especially if it's a new school.
At primary school
You are only likely to be bullied by other people in your year.
At secondary school
It's not 'cool' to bully a year 7, so the sort of kids who do it are often not known bullies. The older kids might look scary, but they often help teachers by keeping an eye out for anyone picking on the new pupils.
If someone bullies you try to remember something unusual about them. Tell a teacher what happened straight away. Describe the bully very carefully.