Here is John Calvin from his Institutes of the Christian Religion expressing a great truth about prayer:
“If we would pray fruitfully, we ought therefore to grasp with both hands this assurance of obtaining what we ask, which the Lord enjoins with his own voice, and all the saints teach by their example. For only that prayer is acceptable to God which is born, if I may so express it, out of such presumption of faith, and is grounded in unshaken assurance of hope. He could have been content with the simple mention of faith, yet he not only added confidence but also fortified it with freedom or boldness, that by this mark he might distinguish from us the unbelievers, who indeed indiscriminately mingle with us in our prayers to God, but by chance. The whole church prays in this way in the psalm: “Let thy mercy be upon us, even as we have hoped in thee” (Psalm. 33:22, Comm.). Elsewhere the prophet lays down the same condition: “In the day when I call, this I know, that God is with me” (Psalm. 56:9 Comm.). Likewise: “In the morning I will make ready for thee, and watch.” (Psalm. 5:3 Comm.). From these words we conclude that prayers are vainly cast upon the air unless hope be added, from which we quietly watch for God as from a watchtower.”
What is He saying? Don’t pray unless you “add hope” that God will answer! Grasp with both hands the truth that God answers prayer, and never let go of that truth. Prayers should always be sent to heaven with an “assurance of obtaining”. Look in particular at the verses Calvin quotes. He is saying that our heavenly Father wants us to be confident in praying; He wants to know that His mercy will be upon us (answers will come) according to how we have hoped in Him.
So pray an “acceptable” prayer today…the kind of prayer which believes a prayer-answering God is hearing you.