If the heart wanders or is distracted, bring it back to the point quite gently -- and even if you do nothing during the whole of your prayer but bring your heart back, though it went away every time you brought it back, your time would be very well employed.
Notice that the more you become a connoisseur of gratitude, the less you are the victim of resentment, depression, and despair. Gratitude will act as an elixir that will gradually dissolve the hard shell of your ego -- your need to possess and control -- and transform you into a generous being. The sense of gratitude produces true spiritual alchemy, makes us magnanimous -- large souled.