"Rest in the LORD, and wait patiently for Him; fret not thyself because of him who prospereth in his way, because of the man who bringeth wicked devices to pass." Psalm 37:7
Fret not means, don't grow angry or jealous or discouraged and get all caught up in what is happening around you or to you. Wait patiently on the Lord. Rest in the inner knowledge that God has it covered, under control, within prescribed parameters, that God is fully aware of your entire situation, yesterday, today and tomorrow and God is working out the details. Fretting does not and cannot bring about any results. It is an emotional response with no efficacy. Trusting God on the other hand, has power in it, in that, trust is built upon faith, and faith is a real substance that does have efficacy.
Keep your focus. You are responsible for your actions, not others. Sometimes what appears to be someone 'prospering in the way' is actually someone being disobedient to God and reaping a few moments of perceived prosperity. But God is with you for the long haul and the long haul is the one that reveals a persons true character and relationship with God. I've seen many Christians jump at any chance to get rich as if getting rich were an honorable goal. Getting rich by honest pursuits, with hard work, personal integrity and godly stewardship is an honorable goal. But getting rich as a goal is not for everyone, nor is it supposed to be or ever was supposed to be part of the Christian manifesto.
There will always be rich Christians, middle income Christians and poor Christians. Finding your place in God's economy and being satisfied there is true riches. Knowing who you are and finding your place in life, whether it is to be as an engineer or doctor, car mechanic, tire salesman, housewife or lawyer is where true riches are born. If it wasn't for all the advertisements you are exposed to everyday, you would already know that riches are within and have nothing to do with material wealth.
You are already anointed to do and to be all that God intended you to be. Keep your eyes on your relationship with God and seek Him out for your answers. Get your eyes off of what others have and you will have nothing to fret about.