Q: What rule hath God given for our direction in prayer?
A: The whole word of God is of use to direct us in prayer; but the special rule of direction is that form of prayer which Christ taught his disciples, commonly called The Lord’s Prayer.

Q: What doth the preface of the Lord’s prayer teach us?
A: The preface of the Lord’s prayer which is, Our Father which art in heaven, teacheth us to draw near to God with all holy reverence and confidence, as children to a father, able and ready to help us; and that we should pray with and for others.

(Questions XCIX and C of the Westminster Shorter Catechism).