To be grateful for the good things that happen in our lives is easy, but to be grateful for all our lives—the good as well as the bad, the moments of joy as well as the moments of sorrow, the successes as well as the failures, the rewards as well as the rejections—that requires hard spiritual work. Still, we are only truly grateful people when we can say thank you to all that has brought us to the present moment.
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.