What hinders prayer?

While performing research for a school project on prayer, I was introduced to a book called How to Pray by R.A. Torrey. Although the book was written more than a century ago, the information in the book is relevant to the life of a Believer today. The first hinderance that Torrey writes of is the hinderance of selfishness. Torrey states on page 66 of the book, "A selfish purpose in prayer robs of power." I had never thought of this subject in this manner. How selfish are we as believers in our prayers? Do we long for what God can give us, or do we long for what God can do through us? What is the purpose of our prayers? Is the purpose to receive for us, or to receive to give to others? When Jesus prayed before his crucifixion, he prayed for his workers and those that were left behind. He prayed for himself, but in that he was doing the will of the Father that had sent him. He wanted the work that he had started and the workers that had been faithful to realize their full potential in God's will. Maybe this is what our prayers should be about.