What authority do we have to lead a prayer? Where in the Bible does it talk about this practice?
I Corinthians 14:26-33 tells us the importance of church services being orderly. People are not to be talking at the same time. In that same discussion there is mention of someone saying "Amen" when another is offering thanks (a prayer). "Otherwise, if you bless with the spirit, how will he who occupies the place of the uninformed say "Amen" at your giving of thanks, since he does not understand what you say?" (I Corinthians 14:16).
We have examples of people leading groups in prayer, such as Solomon offering a prayer at the dedication of the temple (I Kings 8:12ff). Jesus also lead the disciples in prayer at the Lord's Supper (I Corinthians 11:24-25), and we have record of his prayer in John 17 for the disciples.