John Piper gives seven practical suggestions to cultivate gravity and gladness in your preaching:
1. Strive for practical, earnest, glad-hearted holiness in every area of your life.The Supremacy of God in Preaching (p. 60-63).
2. Make your life - especially the life of your study - a life of constant communion with God in prayer.
3. Read books written by those who bleed Bible when you prick them and who are blood earnest about the truths they discuss.
4. Direct your mind often to the contemplation of death.
5. Consider the biblical teaching that as a preacher you will be judged with greater strictness.
6. Consider the example of Jesus. He was as kind and tender and gentle as a righteous man could be.
7. Strive with all your strength to know God and to humble yourself under his mighty hand.