Step 1 - Find big school and college pages on Instagram, preferably big ones.
Step 2 - Put the initials of a school in your bio and follow all of it's followers. Also like one of their old photos to show interest.
Step 3 - Most of these will follow you back thinking you are from the same school/college and then you can unfollow them to keep your ratio up kek
Step 4 - Repeat this process with more schools/colleges to gain more followers