Firstly, pray.
Secondly, fast if, or when, your state in life allows it. It could be diffiucalt being in high school.
Next, you have to use asymmetrical and covert methods to get your peers to hear you. Hand out info to trad websites that are a wealth of info on Church teachings. You don't have to agree with those sites 100% or even 80%, but they can still lead people to holy tradition and help them understand the pitfalls of the Novus Ordo. Make fliers and hand them out. Use sidewalk chalk to write down web adresses or to call attention to a Catholic or moral issue, or a thought-provoking short comment that clears their mind just for a moment so they will question the diabolical status quo. Write incredible but often censored facts on chalk/marker boards, and have the pull down projector screens blocking it, subsequently, when the teacher pulls it up - walla - a truth bomb for everyone to see and a commotion that briefly snaps some people out of their haze and might get them talking about it after class. Form a group.
The faculty and Newchurch roman collar-wearers are too far gone. They might even try to reprimand you. Don't waste your time on them.