What rule hath God given for our direction in the duty of prayer?

The whole word of God is of use to direct us in the duty of prayer;[1] but the special rule of direction is that form of prayer which our Savior Christ taught his disciples, commonly called The Lord’s prayer.[2] 

1. I John 5:14

   And this is the confidence that we have toward him, that if we ask anything according to his will he hears us.

2. Matt. 6:2-13

   “Our Father in heaven,
   hallowed be your name.
   10 Your kingdom come,
   your will be done, 
   on earth as it is in heaven.
   11 Give us this day our daily bread, 
   12 and forgive us our debts,
   as we also have forgiven our debtors.
   13 And lead us not into temptation,
   but deliver us from evil. 

   Luke 11:2-4

   “Father, hallowed be your name.
   Your kingdom come.
   3 Give us each day our daily bread, 
   4 and forgive us our sins,
   for we ourselves forgive everyone who is indebted to us.
   And lead us not into temptation.”

Question 186, Westminster Larger Catechism