Don’t: Tell anyone that you've decided to resign before you have a signed agreement and official start date from your new employer. At best, you’ll look pretty stupid if your new job falls through. At worst, you could motivate your boss to fire you before you have a chance to quit your job again.
Do: Tell your supervisor before you tell your coworkers.
Don’t: Offer too much detail about the new position or your decision to leave. The less you say, the less can be used as leverage against you.
Do: Briefly explain your reason for leaving. Simply saying that you've accepted another job that is more in line with your career goals is enough.