Do not be anxious about anything, but in everything, by prayer and petition, with thanksgiving, present your requests to God.
In a perfect world we would trust God completely and never worry about anything. At the end of Matthew 6, Jesus speaks about worry and implores His listeners to consider how God takes care of the birds of the field. He reminds them that God cares much more for them than the birds of the field.
In reality, we worry from time to time and some people worry more than others. There are lines between wanting to be prepared, concern, and outright worry and they are hard to define. At some point worry becomes sinful because it demonstrates a lack of trust in God.
One of the best ways to defeat worry is to turn to God in prayer. For starters, turning to God in prayer demonstrates that we trust Him to answer our prayers. This turns the focus away from our efforts to solve a particular problem and focuses on God and His ability to handle any problem.
Prayer with thanksgiving goes one step further in eliminating worry. When we give thanks for God, we acknowledge what He has done for us. By remembering what God has done for us, we gain confidence that God will continue to be with us. This helps eliminate worry by building trust in God because we remember everything that He has done in the past.