Starting high school in a month, any advice?

Just as the title says, I'll enter 9th grade as soon as April begins and if you have any academic advice, please let me know. There are also some questions I had -

  1. What is the best reference book for Math's, Science, and SST
  2. Which YouTube channels/teachers are the best and for which subject? I have heard from a cousin that next toppers is good but this sub clearly has..different opinions.

Also, if any of you are planning to study abroad do share some tips/resources/scholarships for the same too because I want to and could probably use it. Thanks!<3