The Scriptural principle that we use when we feel any kind of fear (and we all do from time to time, as fear is a response of the lower nature in all of us) is that of First John 4:18, which says, "Fear and Love cannot exist together, for when Love is made complete, fear is cast outside."
So, each minute of each day, fear is our main enemy. It is Love's opposite; since God is Love, then the "devil" is fear.
In prayer and meditation, picture yourself filled with the bright light of God's Love. Imagine it as a bright gold flowing down from heaven and filling you, entering the top of your head. In time, if you repeat this procedure, Love will crowd out all fear from the heart and mind. Pray to the God of Love with the absolute certainty that He will answer you; for it is His will that all of his children be filled to overflowing with the Light of Love.
This might have no effect if practiced only once or twice; but if you make it a sound, reliable habit, doing it several times a day, with the passage of a little time, you will find the disease of fear starting to retreat. If you practice long enough, one day, the fear will be completely gone, vanished.
God loves you immeasurably, illimitably. His sweet Love is beyond all comprehension. So, add to the exercise discussed above actual acts of Love for yourself and others. Every day, find some way to express Love.
Write an email, visit a friend, do an errand, help an animal, a child, an elderly person, or a challenged person: These, and many other activities, will help you practice the "faith" of true worship, and will strengthen the Love-nature within you. As the Love-nature strengthens, the fear-nature wilts and retreats. Fear vanishes in the Presence of Love. And Love is irresistible.