"But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking." Matthew 6:7
First of all Jesus says "when ye pray." Jesus doesn't say if ye pray. Praying is part of the connection between God and man that God grants. It's not just that your prayer is heard, but if you are born again, inside of you - you have the indwelling Holy Spirit to assist you with what to pray for and how to pray. Now you can see that God says that the heathen, (those who do not have Christ) think that if they pray they will be heard because they pray often and sometimes loudly. The heathen pray out of duty and religious upbringing. It's true, those without Christ pray and many of them pray fervently, some five times a day, some more. The non-Christian world prays and they have religious ceremonies. Entire nations are built upon this premise.
Jesus is instructing believers that when they pray, God does not need to be reminded that He is God, nor does God need to be reminded of anything. Don't use vain repetitions. Why is that important? Because anybody can use vain repetitions and appear to be in touch with God because they pray or they say something religious over and over again. That's not prayer at all. That's religious rhetoric filling the minds of the people with false hope and false belief.
Jesus is instructing you to be real with God. In the presence of no one, speak to God your mind. Ask for wisdom. Seek His face to know Him, not just so that you can get things from God, but to know God personally. When you pray, talk to God. Let God know your frustrations. Talk about your battles, your losses, your pain or your successes. Come boldly before the throne, not cocky as if you knew it all, but boldly, in that God wants to hear from you and it is your turn to speak. Praying is communication with God, not whining and complaining about so and so. Praying is about finding the heart of God on the matter so you can believe it in your heart and go and do God's will.
But what about all the weirdos out there that claim God told them to do this or that? And what about all the people that claim God told them to take or steal or kill or maim in the name of God? Don't be fooled by the tricks of the devil. You, nor anyone else will ever be told to do anything against the Word of God, against mankind or against disrupting or destroying God's creation. Those who are hearing that voice are not hearing the voice of God. They are the heathen. They are the ones that claim God on one hand while slaying innocent children with the other. That is a trick of the devil.
Pray because Jesus says to. I find that time in prayer just confessing my shortcomings and asking for wisdom takes a great deal of time. I find that God enjoys when I come to Him just to come to Him, no agenda, no questions, no preconceived ideas about the moment, just mindfully wandering into the throne of grace and thanking God and praising God and worshiping God.
Another reason that Jesus says "when thou prayest," is because God already knows about your situation. God has already gone before you and made a way. God has already intervened to bring about His will. But you and I, we don't see very far and we need to go to prayer so that we can see with the mind of Christ. Otherwise we could not handle the injustice and the improprieties that come our way. Pray to be filled with understanding about how God wants you to be like Christ. The scriptures make more sense when being like Christ is the goal and not just finding religion.