High School English Help

I'm 22, been subbing for a small private school near me recently to help with grad school (I'm getting my masters in Library and Information Science). So far, I've only subbed for the lower school, but tomorrow I'm subbing for the high school English teacher all day, 7th-12th grades. I was an English major in undergrad so I feel ok about potential material but I've never subbed for high schoolers before and I'm wondering if anyone has any last-minute tips on how to do a good job/not lose control of the classroom. I can be pretty soft-spoken and I don't like getting on to students or getting kids in trouble. I'd be so grateful for any advice!