What Else Should I Do When Resigning? First, out of respect and common courtesy, you would ideally tell your manager in person that you are resigning. If you can't wait for that or work remotely or some other complication prevents that, the telephone is the next best option. You can choose to follow up or accompany that discussion with a formal letter of resignation afterwards, but it would be a rare workplace that would require that formality.
Spot the Signs. According to Alison Green, who writes the blog Ask a Manager, this is common practice for some industries, especially if you're leaving to work for a direct competitor. However, in those situations, you'll likely know it's coming and can prepare accordingly.