Dear Mr./Ms. Bossname,
I am writing to tender my resignation effective immediately. I have accepted a position with another firm.
As is common practice in our industry, I will taking my clients with me. As you know, I landed these customers, who trust in my expertise and experience. I do not foresee any issues on either end, and have no intention of talking negatively about the company with these clients, potential new clients, or anyone else. I simply aim to serve the community to the best of my ability, with as little disruption as possible.
Please let me know if you have any questions.