Thanks for Valuable Experience
Please accept this letter as my notice of resignation, effective __(date)__.
Although I thoroughly enjoyed my position at __(name of firm)__, I feel the time is right for me to move on with my career. I am grateful for the opportunities and experience afforded me and for the many friends that I have made along the way.
Thank you for the opportunity to gain such valuable experience. I wish __(name of firm) __ continued success in all future endeavors.