God uses ordinary people

All of the great men and women of the Bible started their lives as ordinary people. God didn't look for the best looking, the most popular, the smartest, the best educated, the best public speakers, the best leaders, the best behaved. Instead he chose those who were rejected by the world, the young, the uneducated, the worst of sinners and he equipped them do what he called them to do. David was a shepherd, Peter and Andrew were fishermen, Paul was persecuting the church, Mary was just a regular Jewish chick. 

In Exodus chapter three God called Moses to rescue the Israelites from Egypt but Moses said, "I am nobody. How can I go to the king and bring the Israelites out of Egypt? God answered, "I will be with you" (verses 11-12). When that voice in your head tells you you're not smart enough, good enough, popular enough, talented enough to be called by God remember that God will be with you. That is the key, God is with you and helping you to do what he called you to do. He might be calling you to teach Kid's church, to write Christian music, to join the worship team at church, to talk to your school friends about your faith, to raise money for the poor, to visit the lonely - whatever is, he is with you and will help you.