The OT tells us that God hears prayers (Psalm 65:2). However, the NT book of 1 John (5:14-15) qualifies the type of prayers that God hears. Prayer that is divinely efficacious must be offered in accordance with God's will in faith (James 1:5-8). Saying a prayer is not like articulating a magical formula. Prayer works because God answers it, not simply because we utter the right words. Yes, the power of life and death are in the tongue. But God is the one who brings it about that the requests contained in prayers come to fruition: it is not magic (Philippians 4:6-7).
Another fallacious notion under which many minds labor is the mistaken idea that God is comparable to some great Santa Clause in the sky. Some persons might be inclined to think that God dispenses answers to petitionary invocations like the mythical Santa dispenses gifts on December 25. Aside from the fact that Santa does not exist, God is not some great Santa in the sky. Prayer is not about what we can get from God, although he does answer prayers that conform to his will. To the contrary, prayer is about (primarily) what we can do for God. It is about selflessness or about expressing our praise and loyalty to God. As Merold Westphal points out (in his book _God, Guilt, and Death_, page 141), prayer is not a crutch nor a "support system" for those who are weak or cowardly. Prayer "pulls us away from self-preoccupations" or "from an easy support system to a risky surrender."
While I do not mean to suggest that it is wrong or unbiblical to request that God do X or Y, I just want to stress that those making petitions to God must approach him with the right attitude in faith. Our prayers must be in harmony with the will of God and we must have the type of faith that can move mountains. As the writer James states, the prayer of the righteous man or woman avails much.