The Ninth and Tenth Commandments say, "You shall not covet."
But Covet has a mother and her name is Compare. This means that before one can covet, he must first compare. He must compare two things: what God has given him, and what God has given to another. All coveting begins with comparing. Even to compare your present situation with one you'd rather be in, soon leads to the sin of coveting: the desire to have what God has not given you.
Covet has a daughter and her name is Complain. She has no friends. Complaining is always the direct result of coveting, just as coveting is the direct result of comparing. Hold in check your comparing and you will hold in check your coveting and complaining.
Replace all of these C's with Contentment. She is the happy, beautiful daughter of faith and trust in God. But do not stop at thanking God for what He has given you. Thank Him especially for what He has given to others. Pray that God will create in you this kind of heart.