The key to any successful endeavor is faith. As Hebrews 11:6 teaches us faith is knowing that God is and that he is a rewarder of those who diligently seek him. So we know that successful prayer is persistent hence the word diligent used here and the knowledge of who he is. 

"with self consciousness, or failure consciousness, God can never work. God is your help, God is your abundance, God is your success, and God is your victory. If two men do not agree, how can they work together? So to walk and work with God, you must engraft God’s types of consciousness to your own. Renew your mind. Constantly think in terms of success, in terms of victory, and in terms of abundance. When you have completely renewed your thinking process, then you will receive the rhema of God. Boldly assimilate the Word of God into your thinking life. Through prayer produce faith, and through faith you will be able to lift your chin up high."

from "The Fourth Dimension" by Dr. David Yonggi Cho