Dear (Supervisor/HR rep),
I am writing to you today to officially submit my resignation from ABC Company effective (XXX Date). After careful consideration, I have accepted another position in line with my long-term career goals.
Please be assured that I will do all I can to assist in the smooth transfer of my responsibilities before leaving. My experience at (your company) has been rewarding and productive, and I wish only the best for you and the organization.
Thanks again for having me as a part of your team.
Sincerely,
(your name)