I am struggling with jealousy in many areas in my life and in my relationships. Any words of advice for me?
Let's analyze jealousy for a moment. You're jealous of your friend's car. Why? Hers is nicer than yours. You're jealous of a colleague's intelligence. Why? It's greater than yours. You're jealous of your sister's artistic talent. Why? You don't have any yourself.
All jealousy boils down to the same thing. They have something you don't, and it's something you want.
Our Sages have a famous saying, "Who is wealthy? He who is happy with what he has." One who is satisfied with his lot in life does not struggle with jealousy, because he does not desire more than what he has. So your friend has a nicer car than yours. But you're happy with your own. Mr. Big Shot at work is smarter than you. You're content with the intelligence G‑d granted you. You lack artistic talent. You have your own abilities.
So let's refocus. Instead of "how can I stop being jealous?" the question really is, "how can I be happy with what I have?"
This question happens to be fundamental. We believe G‑d is all-knowing and good. All knowing means He has full knowledge of what is best for you to have in life; and good means He will grant you what is best for you to have. If G‑d has not seen fit you to give you that car or house, that means that having that car or house at this point in time is not in your best interests. So what's there to be jealous about?
Obviously, it takes a bit of work to make this line of thinking natural. There's no automatic mental switch. But the result is more than worth the effort.