In "Doctrinal Discussion" William Sillings writes the four following tips for conquering discouragement:

1. Whenever possible fill your mind and heart with praise and thanks to God for what He has already done for you.
2. Consciously dwell upon whatever is true, honest, just, pure, lovely, of good report, virtuous, and praiseworthy — instead of things that are negative and which cause doubts and fears in your life.
3. Fill your mind with scriptures that contain the promises of God to you.
4. Practice believing God to answer prayer when you are not under the test of discouragement.

Source: Studies in the Psalms: Adult Teacher's Insights, page 44.