Prayer's Foundation is the Word of God
All prayer is based on what the Word of God says. If a promise is in the Word of God, it is acceptable for us to pray for it.
For example, healing promises are all through the Bible. That means we can pray for our bodies to be healed.
Psalms 30:2 O LORD my God, I cried unto thee, and thou hast healed me.
Psalms 107:20 He sent his word, and healed them, and delivered them from their destructions.
Isaiah 53:5 But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him, and with his stripes, we are healed.
Jeremiah 17:14 Heal me, O LORD, and I shall be healed; save me, and I shall be saved: for thou art my praise.
1 Peter 2:24 Who his own self bare our sins in His own body on the tree, that we, being dead to sins, should live unto righteousness: by whose stripes ye were healed.
We see by these Scriptures the Lord is willing and able to heal us. By this method of finding a Scripture that addresses our problems or questions, we know God will hear us.
The second requirement to this foundational teaching is, we must add faith to our prayer. God does not answer unfaith-filled prayers.
Hebrews 11:6 But without faith it is impossible to please him: for he that cometh to God must believe that he is and that he is a rewarder of them that diligently seek him.
When we add our trust in God’s ability to perform His promises given to us in the Bible, God answers our prayers. He delights in giving us what we need for life and godliness.