Prayer is very important. There are medical studies linking both prayer and meditation with better health. People who pray on a daily basis have been found to experience lower blood pressure, less stress, stronger immune systems, less depression, to live longer and happier lives, etc... These are great benefits and should not be overlooked, but the reason for prayer is to communicate with, ask for help and forgiveness, and please God.
To pray correctly we must be sincere and pray from the heart. Jesus Christ was angered by the falseness of the local religious leaders and likened them to hypocrites - "And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by men. I tell you the truth, they have received their reward in full. But when you pray, go into your room, close the door and pray to your father, who is unseen. Then your Father, who sees what is done in secret, will reward you. And when you pray, do not keep on babbling like pagans, for they think they will be heard because of their many words. Do not be like them, for your Father knows what you need before you ask him (Mathew 6:5-8). Here Jesus Christ specifically states to pray in quiet, not to rant and babble like many priests and evangelists do. This is not sincere, as they are trying to impress their followers and stroke their egos with their impressive vocabulary. God is infinitely smarter than that and will not be impressed by incantations, repetition, and insincerity. He wants us to pray in private, not for show. God would much rather hear a prayer from someone meek and sincere.
We can pray about anything and there is nothing saying you can't repeat requests. We should pray not only about what troubles us, but also for forgiveness and what we are thankful for - our families, good times, God's help, etc... In Matthew 6:9-15 Jesus Christ gives us a great example of how to pray - The Lord's Prayer - "This then is how you should pray:" 'Our Father in heaven, hallowed be your name, your kingdom come, your will be done on earth as it is in heaven. Give us today our daily bread. Forgive us our debts, as we have forgotten our debtors. And lead us not into temptation, but deliver us from the evil one.' For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins." Jesus Christ implies in the Lord's Prayer that we need to forgive everyone. We have all sinned and all need forgiveness. We also need to be thankful for what God has given us. We may be poor, we may have a terrible boss or financial hardships, but we need to look through this and find the good. There is always some good we can reflect upon.
Prayer can be very benefitial when done correctly as God will actually hear and answer prayers and requests that are sincere, truthful, forgiving, and not full of earthly desires - this is coveting and is one of the ten commandments - "Thou shalt not covet." When our prayers aren't answered, maybe its because we weren't praying for the right reasons or for what we really need. Remember, God knows and sees everything and loves all of us so much that he sent his only son Jesus Christ to die for us and our sins. Let us honor him by praying correctly and for the right reasons.