Many Private or Out-of-State schools require Letters of Recommendation with their applications. A positive Letter of Recommendation (LOR) from a Counselor or an academic teacher gives further evidence of integrity and special skills and can really boost an application.
Personally approach a Teacher/Counselor/Administrator when requesting a LOR. Find out what they need -- Brag Sheet, transcript, etc.
Follow up with an email request and be sure to include deadlines.
Give them PLENTY of advance notice.
If you are applying via CommonApp, be sure to add them as a Recommender so they can submit (and make sure you spell their name correctly or they will not receive the request.)
THANK THEM! With a handwritten note (not with a verbal thank you or an email.) It takes a lot of time and effort to write a thoughtful LOR and teachers/counselors are not required to write them for you.