I’m often asked this question, and the short answer is: “You don’t”.
Jealousy in itself is not a bad thing. There is no such thing as a bad emotion, only a bad response to one. Jealousy is human.
The longer answer is this:
I don’t think the question that should be asked is how to not be jealous. Jealousy is something we all experience from time to time. I think the key is communication and honesty with yourself and your partner. When you feel jealous, decide if it is something you can brush off or not. If you cannot deal with the jealousy on your own, communicate with your partner. Tell them you are feeling jealous, and tell them what has happened that may be contributing to that feeling.
Not only will communicating openly with your partner strengthen your relationship, it will also provide an opportunity to express your doubts and give your partner the opportunity to help you work through it.
Bear in mind, that your jealousy is not your partner’s fault. They may have done something that sparked the jealous fires, but the emotion is not their fault. That is your emotion, and you need to own it. Taking ownership of the emotion does not make it your fault either. It does, however, put the responsibility on you to respond to the emotion in a way that in constructive to your own well-being.
Remember, there are no bad emotions. Only bad responses.