Try to strengthen your mind by reading something that requires effort, thought, and concentration.
Try to do somebody a good turn and not get found out.
Try to do a task that needs to be done, but which you have been putting off.
Try to go for one full day without finding fault in anything.
Try to have a quiet half-hour by yourself. Think of God, read the Bible; You'll get a little more perspective in your life.
Don't be afraid to be happy; enjoy what is beautiful; believe that those you love, love you.