If you are given the task to lead the congregation in prayer on Sunday morning, I encourage you to consider the following:
1) You are the representative of the people -- bringing their prayers and the concerns of their hearts before the Father. It is not just your own personal prayer -- so instead if saying, "God, I love you so much" say, "God, we are here to tell you how much we love you."
2) Be sure you don't pray the same phrases every time. Change it up. If you don't prepare and think about the prayer, you will automatically resort to old familiar cliches -- which wear out quickly in public usage.
3) Say "thank you" to God early in the prayer. "O Lord, we thank you today for providing strength, peace, and contentment for each moment. . ."
4) Don't preach at the congregation through the prayer. Don't yell. God is not hard of hearing.
5) If you use an ancient or other written prayer -- let it stand alone. Don't add to it. If it's worth using, then it shouldn't need your help to boost it. Trying to add your own topping to a classic prayer is like adding a little color to the Mona Lisa with magic marker. This is also true with the Lord's Prayer -- don't recite the Lord's Prayer, and then try to improve on it.
6) Whenever possible, add a personal element to the prayer -- one who is sick in the hospital, one who has lost a loved one this week, students going back to school. In many ways, a pastoral prayer is an act of pastoral care. Be careful, though, not to belabor this or to go into details. God already knows all the details. Something like this would be appropriate, "Father, we ask that you would comfort the Lewis family as they grieve the loss of Larry, their beloved husband and father, We pray also that you would bring healing to our friend, Judy, in the hospital and we remember Josh today, as he serves in Iraq." The prayer is not an announcement, but rather as a connecting point with those who are hurting.
Just a quick mention will bless all the friends and loved ones, as well as the person named in the prayer. (They'll hear about it.)
7) Eliminate distracting mannerisms. i.e. repeating the same word or phrase over and over -- "Dear Lord, oh God, we thank you, Dear Lord, oh God, for helping us, Dear Lord, oh God." Another common repeat is "just wanna" -- "Dear God, we just wanna praise you tonight, and we just wanna give you all the glory. . .
8) Occasionally, lead them in a guided silent prayer. "First, let's pray for our loved ones". . . then allow for a period of silence, while they do so. Be sure to give adequate time for this. A common mistake is breaking the silence too quickly.
9) Don't use a special "prayer voice". Don't pray in 17th century English. Don't say "UH" at the end of every sentence. "Dear God-uh, We are in your presence today-uh to give you praise-uh."
10) Along the same line, be sure to speak clearly and loud enough so the people can hear you. Don't mumble into your shirt. Keep you head up enough to project.
11) Keep it brief. The impact and helpfulness of a public prayer diminishes with long, eloquent waxing. It's better to do your long prayers in private -- and keep your public prayers short.
12) Finish the prayer in Jesus' Name. Say it clearly and deliberately -- "In Jesus' name, amen" or "In the mighty name of Jesus, amen", or "In the name of our Savior, Jesus, amen." Speak his name boldly and clearly as you finish the prayer.
13) Through it all, remember that you are addressing God -- not the people. (Your job is not to make an impression) But, you are addressing God on behalf of the people.