Respond to being put on the waitlist at a certain college by letting that school know you’d like to stay on the waitlist. This is usually done through the admissions portal or by email.

Let your guidance counselor know that you are waitlisted at that certain school and that it is your top choice. He may call the school on your behalf.
Contact your Admissions Rep and let him know that the college is your top choice and that you would attend if offered a spot in the incoming class. This can be done via email or through your admissions portal.
Make sure to deposit at a school that you were accepted to by May 1st. Waitlists vary in movement. There are a lot of variables as to why a student is or is not offered a spot off the waitlist. Institutions wait to see what their enrollment looks like before determining if they will need to use their waitlist after May 1st.