St. Theophan the Recluse: Always pray as if just beginning

You must never regard any spiritual work as firmly established, and this is especially true of prayer; but always pray as if beginning for the first time. When we do a thing for the first time, we come to it fresh and with a new-born enthusiasm. If, when starting to pray, you always approach it as though you had never yet prayed properly, and only now for the first time wished to do so, you will always pray with a fresh and lively zeal. And all will go well.
If you are not successful in your prayer, do not expect success in anything. It is the root of all.
+St. Theophan the Recluse, from What is Prayer? Chapter 2 in The Art of Prayer: An Orthodox Anthology, compiled by Igumen Chariton of Valamo.