You can ask for anything in My name, and I will do it, so that the Son can bring glory to the Father. John 14:13 NLT
"It is the answer to prayer which makes praying a power for God and for man and makes praying real and divine. Unanswered prayers are training schools for unbelief, an imposition and a nuisance, an impertinence to God and man." E.M. Bounds
One way in which we can know that God hears our prayers is by getting answers.
Some people pray this way, "Lord, I pray that..." And then get out of prayer with no expectations whatsoever. It's kind of like ordering a burger in McDonald's and after you've placed your order, you turn around, leave, forget about it and never come back. You get what you asked for but don't receive it.
God is not some mystical, make believe creature. He's a living person who has power over everything in creation. He's not deaf. When we pray, He hears. But when we pray, we have to be in an attitude of expectation. We have to have it in our hearts that God delights in answering our prayers: whether the answer is yes, wait, or no because He has something better.
Quoting from E.M. Bounds again, "To God and to man, the answer to prayer is the all-important part of our praying." The answer to prayer, direct and unmistakable, is the evidence of God's being. It proves that God lives, that there is a God, an intelligent being, who is interested in His creatures, and who listens to them when they approach Him in prayer. There is no proof so clear and demonstrative that God exists than prayer and its answer.
"This was Elijah's plea: 'Hear me, O Lord, hear me, that this people may know that thou art the Lord God.' (1 Kings 18:37)"
God is glorified when our prayers are answered. It proves that He exists, and that's what we want all the world to know.
Prayer is not about fancy words or rituals. The length of the prayer is not even the case. God prefers a genuine heart rather than a performance of poetry prayers.
I'm quoting from E.M. Bounds yet again, "Elijah might have prayed on Carmel's heights till his good day with all the fire and energy of his soul, and if no answer had been given, no glory would have come to God. Peter might have shut himself up with Dorcas's dead body till he himself died on his knees, and if no answer had come, no glory to God nor good to man would have followed, but only doubt, blight, and dismay."
When we approach God, let us approach boldly and expect Him to answer. He will answer, He always does.
When we thank Him for an answer, He is glorified. When we praise Him for an answer, He is glorified. When we tell others about what God has done for us, He is glorified. So, I suggest, let us be daring in our asking, not forgetting to pray in accordance to His will which is good, pleasing and perfect, and expect to see answers.