"One way to re-collect the mind easily in the time of prayer, and preserve it more in tranquillity, is not to let it wander too far at other times: you should keep it strictly in the presence of GOD; and being accustomed to think of Him often, you will find it easy to keep your mind calm in the time of prayer, or at least to recall it from its wanderings."

from the Eighth Letter, "The Practice of the Presence of God" - Brother Lawrence