Prayer is the offering of our desires unto God in the name of Christ, by the help of the Holy Spirit, with confession of sins and thankful acknowledgement of his mercies. The Reformed tradition emphasizes praying with reverence for God's majesty, a sincere sense of our own unworthiness, and a confident faith that God will hear us for Christ's sake.
Prayer is not merely a ritual, but an essential exercise of faith where we offer our desires to God for things agreeable to his will, always in the name of Christ (Westminster Shorter Catechism — Question 98). We are not left to our own devices regarding how to approach the throne of grace; the whole Word of God directs us, with The Lord's Prayer serving as our special rule of direction (Westminster Shorter Catechism — Question 99).
Acceptable prayer requires a deep, awful apprehension of the majesty of God balanced by a profound sense of our own unworthiness and sin (Westminster Larger Catechism — Question 185). As the Heidelberg Catechism — Question 117 instructs, we must pray from the heart to the one true God, knowing our need, and remaining fully persuaded that for the sake of Christ, God will certainly hear us.
We are more sinful than we dared believe, and yet, because of Christ, we are more loved than we dared hope. Our prayers are sanctified solely because Christ is our Mediator. Since we do not know how to pray as we ought, the Holy Spirit helps our weakness: "And in like manner the Spirit also helpeth our infirmity: for we know not how to pray as we ought; but the Spirit himself maketh intercession for us with groanings which cannot be uttered" (Romans 8:26). According to the Institutes of the Christian Religion, this is a perpetual exercise of faith where we look beyond our own merits to the inexhaustible fountain of Christ's righteousness.