If you are switching jobs:
The replacement of job should not be an excuse for labelling the workplace you have worked in as poor. You should show your boss why you're leaving the company and you should point out the things that bothered you, take action in a polite and professional method however. Keep a way of measuring professionalism which has led one to this correct point in your career. This can help you to make strong references later on. In conversations with new potential employers, it's important to be expert.
You should also tell your first-class that you are grateful for the chance which you have had in working for his or hers business. You won't ever know when your current boss will end up being a great reference. Remember that no one likes to be criticized. Not from subordinates or co-workers. Even if they are worthy of it. A person with whom you have ever worked with can be a possibly positive reference. Usually do not demolish the bridges behind you. Maintain genuine contacts.