Some traditions use set prayers. Others rely on extemporaneous prayers. Both have their place. But I believe what our congregations need most are studied prayers, well prepared, well expressed. These prayers may or may not be read, but will be thought through ahead of time. Publicly leading a church in prayer deserves thoughtful preparation.
1. Use forms with freedom. Learn from The Valley of Vision or Hughes Oliphant Old or the Book of Common Prayer. But suit their prayers to your own purposes. The Didache, after laying down set prayers for Communion, also allows "the prophets to give thanks however they wish."
2. Pray Scripture. Don't just ask God for what we want. Let him teach us what we should want.
3. Don't footnote. Charles Spurgeon: "It is not necessary in prayer to string a selection of texts of Scripture together, and quote David, and Daniel, and Job, and Paul, and Peter, and every other body, under the title of 'thy servant of old.'" The Lord already knows who said everything, so don't tell him again in your prayers.
4. Leave the preaching for the sermon. Don't exhort. Don't explain texts. Don't unpack complex theology. Spurgeon again: "Long prayers either consist of repetitions, or else of unnecessary explanations which God does not require; or else they degenerate into downright preachings, so that there is no difference between the praying and the preaching, except that in the one the minister has his eyes shut, and in the other he keeps them open. It is not necessary in prayer to rehearse the Westminster Assembly's Catechism."
5. Share some details of congregational life, but not all. A good shepherd will often mention by name various sheep that ...